Implemented joystick input.

I had to redo how input is done entirely, so more than one source of input can be used for game inputs.

I added new inputs, menu_decide and menu_back. Return and escape still have their reserved status, sending menu_decide and menu_back, respectively. Other keys are reserved too, like arrows, to ensure users can always reconfigure input.

scene.lua

@@ -5,7 +5,8 @@ Scene = Object:extend()
 function Scene:new() end
 function Scene:update() end
 function Scene:render() end
-function Scene:onKeyPress() end
+function Scene:onInputPress() end
+function Scene:onInputRelease() end
 
 ExitScene = require "scene.exit"
 GameScene = require "scene.game"