Rotatris

New mode! Rotatris: 2 new buttons for rotating the board; clear rings on a square board instead of lines; pieces spawn in the middle

Many misc fixes and improvements including color changes (help I'm colorblind), more DAS consistency, and ghost pieces.

Graphics update

• lightly highlight the active piece (just making it a bit brighter around the border)
• line clear animations (one for less than 4 lines cleared, another for 4 lines cleared)
• it is now easier to quit to the main menu while in the pause screen

Fully functional (mostly)

Features:

• Gamepads (with custom layouts in Linux requiring no extra programs; see README.md)
• Custom-mapped keyboard control layouts
• Any number of players 1-62
• A bunch of little things that aren't necessarily trivial, but are sort of just expected to be there

Missing features:

• Using mouse for the menu
• Saving highscores
• Saving keyboard control layouts
• Music/sounds
• Netcode