libgosu 0.8.5

http://libgosu.org

Compile libgosu as a .dylib
See formula comment for details

No pkg-config .pc file yet
libgosu 0.8.5 formula fixups

Cleaned up the formula code according to mikemcquaid's suggestions.

However, the build is still not yet officially supported upstream.
libgosu: add 0.8.5 bottle.