Makefile improvements

 * Separated bin/lib install path. It is mainly done for homebrew, which requires placing bin/lib into different directories. (See the discussion at Homebrew/homebrew#27152)
 * Minor change of using `$(OUTPUT)` instead of `haxe.exe` in clean_haxe

It works for me, but since I'm not fluent in Makefile, so it would be great if you can take a look before merging.