music.0

This release mainly adds multi-channel sfx + music. Celeste is now playable... a bit slow, but playable.

• P8SCII
  • Special character replacement (\123)
  • \n \r \b
  • background color #
  • ★ and ○ characters
• pico-8 predefined functions:
  • music
  • extcmd (reset, pause, shutdown)
  • fget
  • fset
  • atan2
  • ceil
  • pset
  • shr
  • shl
  • sgn
  • count
• Improve pico-8 lua transform
• sfx offset, length and loops
• squish sprites
• flip sprites
• btnp delay config through poke
• map layers
• improve render performance (will need more work)
• reset cart from pause menu
• add many button aliases for X and O