Plugin generators

[davesmith00000]

Provide a series of source generators to make working with Indigo and it's assets easier. This PR includes:

• Config: Generates a Scala module with a GameConfig instance that is synchronised with your build settings (view port and background colour).
• Asset listing: Generates a Scala moduke listing all your assets, respects folder structure, and provides helpers like sets of assets to load and accompanying simple materials etc.
• Embed text: ...from any text file into a Scala module.
• Embed GLSL shader pairs: Takes a vertex and fragment shader pair and embeds them into a Scala module
• Data: Embed's (for instance) CSV or Markdown tables as either Enum's or Maps
• Aseprite data: Can also be embedded directly into a Scala module

[davesmith00000]

I think this is there now, I'm going to test it on the Roguelike to double check it works as expected.

[davesmith00000]

This has been tested and extensively expanded / improved through the process of using it on the roguelike in this PR: davesmith00000/roguelike#30