Filter diagonal presses

[pinobatch]

Gikkman on Twitch played Libbet and got frustrated with bonking (inputting an invalid move) when pressing diagonally. Because this is a 4-way game, the game should treat a diagonal press as if the Control Pad were in the same position as last frame.

[pinobatch]

ISSOtm recommended to prioritize the inputs in this order:

1. Same direction
2. Opposite direction, as 180-degree turns (e.g. roll left then jump right) are more common in this game than in many other 4-way grid games
3. 90 degrees different

[ISSOtm]

And I'd recommend treating U+D/L+R as if neither was held. (I usually do so directly in my input polling routine.)