Improvement to onboarding new players.
Highlights:
- Revamp instructions with visual aids and add tutorial floor "Closet"
- Wait before detecting Super Game Boy
- Correct note periods to concert pitch
- Make shadow during jump more visible
- SGB, GBC: Lighten green to reduce Helmholtz-Kohlrausch illusion
- SGB: make border tile 0 transparent to reduce flash during fade
- Add an experimental way of allocating subroutines local variables, using a new feature of RGBDS 0.7
- Allow building with out-of-tree RGBDS for regression testing (RGBDS 0.7 includes this project as a test case! gbdev/rgbds#1260)