Require rubysl on Rubinius 2.2
Improve method names for ArgumentBuilder
Remove last traces of the inarg method
Move and rename #retval to ArgumentBuilder
Remove BaseArgumentBuilder#retname
Use same sort order for methods for all argument builders
Refactor ArgumentBuilder#pre_conversion
Avoid needless assignment in post conversion
Treat skipped arguments more like regular arguments
Add tests for callback out arguments
Use argument infos with correct direction for signal and callback builders
Always do pre-conversion in CallbackArgumentBuilder
Handle callback arguments with direction :out