renamed <freetype/config/ft2build.h> to 'ftheader.h' to avoid
name conflicts with top-level <ft2build.h>

added some comments for docmaker in ftheader.h in order to
document the header file macros..
diff --git a/include/ft2build.h b/include/ft2build.h
index 3da8add..cd94c00 100644
--- a/include/ft2build.h
+++ b/include/ft2build.h
@@ -31,7 +31,7 @@
 #ifndef __FT2_BUILD_GENERIC_H__
 #define __FT2_BUILD_GENERIC_H__
 
-#include <freetype/config/ft2build.h>
+#include <freetype/config/ftheader.h>
 
 #endif /* __FT2_BUILD_GENERIC_H__ */