Holiday 2020 Update

Content Changes:
+ added a new boss, Thorn
+ added a dramatic intro with detailed and mostly-finished portraits for most bosses
+ added new characters: Orca, Dreamer, Sheila, Marquis
+ added the Gallery Park Interior level (accessible from the subway station)
~ the Gallery Park subway stop looks different
~ The Deeps has a lever-based closed shortcut that explicitly reroutes players through the Sludge Temple
~ redid the tutorial area
+ added a more dramatic death animation
+ added pickups that refresh aerial movement (look for a wing icon inside a circle)
+ added in-depth control rebind options. note that in-game glyphs still reflect the default buttons; I'll fix this later

Gameplay Changes:
- parrying now uses energy proportional to the deflected attack's damage
+ parrying an attack now turns you towards your attacker
- Val can only dash once in the air, dash is refreshed by touching a surface or a movement refresh pickup
+ dash availability is signified by wing color (red = unavailable)
- Val can only divekick once in the air (refreshes in the same way as dash)
+ added a new ability (Surf) but it's unusable at the moment
~ changed Richter's unlockable bat attack to a down-air punch
+ input buffer length option
+ sound mixing changes
+ added D-pad UI navigation and movement
+ added an option to let the game run in the background

Visual Changes:
+ camera centers both player and boss during boss fight

Bugfixes:
- too many to count, honestly
- let me know if I missed any

Internal refactors:
+ used xNode graphs for attacks
+ wrote a custom buffer system
+ used Rewired for input mapping