Merge pull request #91 from marcelotrevisani/patch-1

Possibility to specify a different PREFIX
diff --git a/Makefile b/Makefile
index a7850a2..f91f626 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-PREFIX=/usr/local
+PREFIX?=/usr/local
 INSTALL_DIR=$(PREFIX)/include/xbyak
 
 all: