New input types

[Geokureli]

Various ideas for types of input types:

• MouseScreenEdge(axis, distance:Float): x is 1.0 when the mouse is within distance pixels from the right edge, and -1.0 on the left side, similar y for top and bottom (1.0 for top). Often used in RTS games with large maps, i.e. Civ and Warcraft
• CustomAnalog(x:()->Float, y:()->Float): Allows any custom analog input, useful for Flesh to Stone's on-screen mobile analog stick, or anything not covered by existing commands. Alternatively (or additionally), can be CustomAnalog(input:FlxActionInputAnalog), might not be possible to do with @:inputs tags
• CustomDigital: Same as above but for digital, either CustomDigital(pressed:()->Bool) or CustomDigital(input:FlxActionInputDigital) or whatever
• Input(input:IFlxInput): Allows attaching buttons, say if PAUSE uses a gamepad button on desktop but an on-screen button for mobile
• add deadzone and axis to analog sticks