Created 'yape', added a `Manager` and reworked Components

The main changes are:
* Separation of razzytails code from generic, game engine code in '/yape'
* Renamed Asset/LoadableAsset to Component/LoadableComponent to avoid confusion with images, fonts, JSON files, and sounds, which are collectively called 'assets'.
* Added a Manager class, that handles loading images, JSON files and so on, and caches them in weak reference dictionary. In this way, we don't have to worry about multiple component instances referencing the same asset and reloading the same file repeatedly or freeing them once they are no longer needed.
* Added *_fields methods so that images, fonts and other assets are loaded on behalf of a component automatically. (No more manual load_image() or load_font() calls)
* Added a 'post_process' method for Components as an overideable hook that doesn't need a call to super(). In this way, anything that needs to happen after the Component is loaded can be done in one place.

See the added release notes for more details