Lowlevel exposed

[WilliamDue]

This pull request extends the lowlevel backend to be more suitable for DIKUArcade.

The pull request adds:

• A window class which allows for instantiating multiple windows and different ways of treating Events.
• Drawing functions which are more suited for usage through C#.
• A set of events suited for DIKUArcade.
• Made certain functions and types private if they are not used outside the module.