Prepare to release 0.4.0

tools/version.h

diff --git a/tools/version.h b/tools/version.h
index 6125a73..53df138 100644
--- a/tools/version.h
+++ b/tools/version.h
@@ -9,6 +9,6 @@
 #ifndef BROTLI_TOOLS_VERSION_H_
 #define BROTLI_TOOLS_VERSION_H_
 
-#define BROTLI_VERSION "0.3.0"
+#define BROTLI_VERSION "0.4.0"
 
 #endif  /* BROTLI_TOOLS_VERSION_H_ */