First pass at adding a Manager class, that loads assets and stores weak
references to them for other objects to use. This will help centralize the
storing and retrieval of assets in memory, so many objects can share
references to the same resource without regard to how it is obtained/freed
Merge branch 'refactor/engine-folder' of https://github.com/calebsmith/razzytails into refactor/engine-folder
Moved new manager module to the correct directory structure introduced
in the previous commit