dylib_manager, objc literals, some bug fixes, docs...

This PR contains dylib_manager implementation, objective c literals equvivalent implementation, some bug fixes, and with this PR we have improved docs. I added quite a lot documentation, but it is not finished, there are still parts of pyobjus which are undocumented. 

I'm waiting for Apple to get available services for registering as developer (deploying on device with kivy-ios), because they are currently unavailable.