ci: Rename the ci_* scripts

Give the CI scripts new names that better reflect what they do, and
make room for activities such as linting or dependency installation:
 * Rename ci_autotools.sh to ci_verify_configure.sh.
 * Rename ci_cmake.sh to ci_verify_cmake.sh.
 * Rename ci_legacy.sh to ci_verify_makefiles.sh.

Also rename CI_LEGACY_MAKEFILES to CI_MAKEFILES.

Update the config files for Travis CI and AppVeyor CI accordingly.
diff --git a/.appveyor.yml b/.appveyor.yml
index 88dc11e..f447877 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -28,16 +28,16 @@
       AUTOMATION: cmake
       ARCH: x86_64
     - TOOLCHAIN: msys2
-      AUTOMATION: autotools
+      AUTOMATION: configure
       ARCH: i686
     - TOOLCHAIN: msys2
-      AUTOMATION: autotools
+      AUTOMATION: configure
       ARCH: x86_64
     - TOOLCHAIN: msys2
-      AUTOMATION: legacy
+      AUTOMATION: makefiles
       ARCH: i686
     - TOOLCHAIN: msys2
-      AUTOMATION: legacy
+      AUTOMATION: makefiles
       ARCH: x86_64
 
 install:
@@ -57,13 +57,13 @@
   - 'set CI_CMAKE_BUILD_FLAGS=--parallel 2'
   - 'set CI_CTEST_FLAGS=--parallel 2'
   - 'set CI_MAKE_FLAGS=-j2'
-  - 'set CI_LEGACY_MAKEFILES=scripts/makefile.gcc scripts/makefile.msys scripts/makefile.std'
+  - 'set CI_MAKEFILES=scripts/makefile.gcc scripts/makefile.msys scripts/makefile.std'
 
 build_script:
-  - 'if "%TOOLCHAIN%"=="vstudio" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_cmake.sh"'
-  - 'if "%TOOLCHAIN%"=="msys2" if "%AUTOMATION%"=="cmake" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_cmake.sh"'
-  - 'if "%TOOLCHAIN%"=="msys2" if "%AUTOMATION%"=="autotools" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_autotools.sh"'
-  - 'if "%TOOLCHAIN%"=="msys2" if "%AUTOMATION%"=="legacy" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_legacy.sh"'
+  - 'if "%TOOLCHAIN%"=="vstudio" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_verify_cmake.sh"'
+  - 'if "%TOOLCHAIN%"=="msys2" if "%AUTOMATION%"=="cmake" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_verify_cmake.sh"'
+  - 'if "%TOOLCHAIN%"=="msys2" if "%AUTOMATION%"=="configure" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_verify_configure.sh"'
+  - 'if "%TOOLCHAIN%"=="msys2" if "%AUTOMATION%"=="makefiles" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_verify_makefiles.sh"'
 
 cache:
   - C:\tools\vcpkg\installed
diff --git a/.travis.yml b/.travis.yml
index 70457cd..c48df08 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -17,11 +17,11 @@
   - AUTOMATION=cmake CI_NO_TEST=1
   - AUTOMATION=cmake CI_CMAKE_VARS="-DPNG_HARDWARE_OPTIMIZATIONS=ON" CI_SANITIZERS="address,undefined"
   - AUTOMATION=cmake CI_CMAKE_VARS="-DPNG_HARDWARE_OPTIMIZATIONS=OFF" CI_SANITIZERS="address,undefined"
-  - AUTOMATION=autotools CI_NO_TEST=1
-  - AUTOMATION=autotools CI_CONFIGURE_FLAGS="--enable-hardware-optimizations"
-  - AUTOMATION=autotools CI_CONFIGURE_FLAGS="--disable-hardware-optimizations"
-  - AUTOMATION=legacy CI_NO_TEST=1
-  - AUTOMATION=legacy CI_SANITIZERS="address,undefined"
+  - AUTOMATION=configure CI_NO_TEST=1
+  - AUTOMATION=configure CI_CONFIGURE_FLAGS="--enable-hardware-optimizations"
+  - AUTOMATION=configure CI_CONFIGURE_FLAGS="--disable-hardware-optimizations"
+  - AUTOMATION=makefiles CI_NO_TEST=1
+  - AUTOMATION=makefiles CI_SANITIZERS="address,undefined"
 
 matrix:
   include:
@@ -39,7 +39,7 @@
   - 'export CI_CTEST_FLAGS="--parallel 2"'
   - 'export CI_MAKE_FLAGS=-j2'
   - 'export CI_CC=$TRAVIS_COMPILER'
-  - 'export CI_LEGACY_MAKEFILES="scripts/makefile.$TRAVIS_COMPILER scripts/makefile.std"'
+  - 'export CI_MAKEFILES="scripts/makefile.$TRAVIS_COMPILER scripts/makefile.std"'
 
 script:
-  - './ci/ci_$AUTOMATION.sh'
+  - './ci/ci_verify_$AUTOMATION.sh'
diff --git a/ci/ci_cmake.sh b/ci/ci_verify_cmake.sh
similarity index 99%
rename from ci/ci_cmake.sh
rename to ci/ci_verify_cmake.sh
index 71af270..a92e628 100755
--- a/ci/ci_cmake.sh
+++ b/ci/ci_verify_cmake.sh
@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -e
 
-# ci_cmake.sh
+# ci_verify_cmake.sh
 # Continuously integrate libpng using CMake.
 #
 # Copyright (c) 2019-2022 Cosmin Truta.
diff --git a/ci/ci_autotools.sh b/ci/ci_verify_configure.sh
similarity index 92%
rename from ci/ci_autotools.sh
rename to ci/ci_verify_configure.sh
index 0728540..df82206 100755
--- a/ci/ci_autotools.sh
+++ b/ci/ci_verify_configure.sh
@@ -1,8 +1,8 @@
 #!/usr/bin/env bash
 set -e
 
-# ci_autotools.sh
-# Continuously integrate libpng using the GNU Autotools.
+# ci_verify_configure.sh
+# Continuously integrate libpng using the configure script.
 #
 # Copyright (c) 2019-2022 Cosmin Truta.
 #
@@ -13,8 +13,8 @@
 CI_SCRIPTNAME="$(basename "$0")"
 CI_SCRIPTDIR="$(cd "$(dirname "$0")" && pwd)"
 CI_SRCDIR="$(dirname "$CI_SCRIPTDIR")"
-CI_BUILDDIR="$CI_SRCDIR/out/autotools.build"
-CI_INSTALLDIR="$CI_SRCDIR/out/autotools.install"
+CI_BUILDDIR="$CI_SRCDIR/out/configure.build"
+CI_INSTALLDIR="$CI_SRCDIR/out/configure.install"
 
 function ci_info {
     printf >&2 "%s: %s\\n" "$CI_SCRIPTNAME" "$*"
@@ -32,7 +32,7 @@
     "$@"
 }
 
-function ci_init_autotools {
+function ci_init_configure {
     CI_SYSTEM_NAME="$(uname -s)"
     CI_MACHINE_NAME="$(uname -m)"
     CI_MAKE="${CI_MAKE:-make}"
@@ -44,7 +44,7 @@
     [[ ! $CI_MAKE_VARS ]] || ci_err "unexpected: \$CI_MAKE_VARS='$CI_MAKE_VARS'"
 }
 
-function ci_trace_autotools {
+function ci_trace_configure {
     ci_info "## START OF CONFIGURATION ##"
     ci_info "system name: $CI_SYSTEM_NAME"
     ci_info "machine hardware name: $CI_MACHINE_NAME"
@@ -80,7 +80,7 @@
     ci_info "## END OF CONFIGURATION ##"
 }
 
-function ci_build_autotools {
+function ci_build_configure {
     ci_info "## START OF BUILD ##"
     # Export the configure build environment.
     [[ $CI_CC ]] && ci_spawn export CC="$CI_CC"
@@ -108,10 +108,10 @@
     ci_info "## END OF BUILD ##"
 }
 
-ci_init_autotools
-ci_trace_autotools
+ci_init_configure
+ci_trace_configure
 [[ $# -eq 0 ]] || {
     ci_info "note: this program accepts environment options only"
     ci_err "unexpected command arguments: '$*'"
 }
-ci_build_autotools
+ci_build_configure
diff --git a/ci/ci_legacy.sh b/ci/ci_verify_makefiles.sh
similarity index 90%
rename from ci/ci_legacy.sh
rename to ci/ci_verify_makefiles.sh
index cfe1f53..17658f7 100755
--- a/ci/ci_legacy.sh
+++ b/ci/ci_verify_makefiles.sh
@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -e
 
-# ci_legacy.sh
+# ci_verify_makefiles.sh
 # Continuously integrate libpng using the legacy makefiles.
 #
 # Copyright (c) 2019-2022 Cosmin Truta.
@@ -31,7 +31,7 @@
     "$@"
 }
 
-function ci_init_legacy {
+function ci_init_makefiles {
     CI_SYSTEM_NAME="$(uname -s)"
     CI_MACHINE_NAME="$(uname -m)"
     CI_MAKE="${CI_MAKE:-make}"
@@ -44,23 +44,23 @@
     CI_CC="${CI_CC:-cc}"
     case "$CI_CC" in
     ( *clang* )
-        CI_LEGACY_MAKEFILES="${CI_LEGACY_MAKEFILES:-"scripts/makefile.clang"}" ;;
+        CI_MAKEFILES="${CI_MAKEFILES:-"scripts/makefile.clang"}" ;;
     ( *gcc* )
-        CI_LEGACY_MAKEFILES="${CI_LEGACY_MAKEFILES:-"scripts/makefile.gcc"}" ;;
+        CI_MAKEFILES="${CI_MAKEFILES:-"scripts/makefile.gcc"}" ;;
     ( cc | c89 | c99 )
-        CI_LEGACY_MAKEFILES="${CI_LEGACY_MAKEFILES:-"scripts/makefile.std"}" ;;
+        CI_MAKEFILES="${CI_MAKEFILES:-"scripts/makefile.std"}" ;;
     esac
     CI_LD="${CI_LD:-"$CI_CC"}"
     CI_LIBS="${CI_LIBS:-"-lz -lm"}"
 }
 
-function ci_trace_legacy {
+function ci_trace_makefiles {
     ci_info "## START OF CONFIGURATION ##"
     ci_info "system name: $CI_SYSTEM_NAME"
     ci_info "machine hardware name: $CI_MACHINE_NAME"
     ci_info "source directory: $CI_SRCDIR"
     ci_info "build directory: $CI_BUILDDIR"
-    ci_info "environment option: \$CI_LEGACY_MAKEFILES: '$CI_LEGACY_MAKEFILES'"
+    ci_info "environment option: \$CI_MAKEFILES: '$CI_MAKEFILES'"
     ci_info "environment option: \$CI_MAKE: '$CI_MAKE'"
     ci_info "environment option: \$CI_MAKE_FLAGS: '$CI_MAKE_FLAGS'"
     ci_info "environment option: \$CI_MAKE_VARS: '$CI_MAKE_VARS'"
@@ -90,7 +90,7 @@
     ci_info "## END OF CONFIGURATION ##"
 }
 
-function ci_build_legacy {
+function ci_build_makefiles {
     ci_info "## START OF BUILD ##"
     # Initialize ALL_CC_FLAGS and ALL_LD_FLAGS as strings.
     local ALL_CC_FLAGS="$CI_CC_FLAGS"
@@ -118,7 +118,7 @@
     # Build!
     ci_spawn cd "$CI_SRCDIR"
     local MY_MAKEFILE
-    for MY_MAKEFILE in $CI_LEGACY_MAKEFILES
+    for MY_MAKEFILE in $CI_MAKEFILES
     do
         ci_info "using makefile: $MY_MAKEFILE"
         ci_spawn "$CI_MAKE" -f "$MY_MAKEFILE" \
@@ -138,10 +138,10 @@
     ci_info "## END OF BUILD ##"
 }
 
-ci_init_legacy
-ci_trace_legacy
+ci_init_makefiles
+ci_trace_makefiles
 [[ $# -eq 0 ]] || {
     ci_info "note: this program accepts environment options only"
     ci_err "unexpected command arguments: '$*'"
 }
-ci_build_legacy
+ci_build_makefiles