Crate generic_asset

This Wizardry is courtesy of Tantan and updated to 0.12.1 by me

This is based on https://www.youtube.com/watch?v=ModFC1bhobA&t=403s?

Macros

• create_asset_loader
  a macro to create a generic asset loader for ron files in bevy 0.12.1

Enums

• CustomAssetLoaderError
  An error type for the asset loader