extended 'flatten' api documentation
Update AssetManager.as

get the correct extension with url like this:
"abc/xyz.extension?get_param=something"
Merge pull request #325 from peerobo/patch-2

AssetManager now gets correct extension in urls like this: 'abc/xyz.ext?param=something'
Merge branch 'master' of https://github.com/PrimaryFeather/Starling-Framework into performance