Multiplayer- Focused Update (v0.006a)

I noticed in my referral links that I was getting people searching for local multiplayer and keyboard controls in particular, so I added keyboard controls for 2 players on the same keyboard and a larger level to accommodate more players (though it works fine with 1 player too).

I also added an "experimental control style".  The actual controls are the same, but the bird handles differently, with a higher top speed, but accelerating and decelerating gradually, making it a bit harder to handle.  I think it's more fun, but please let me know what you think!  I plan to keep both modes available and maybe make more bird "builds" for people to choose from.

Combos are now handled separately for each player and represented by "sparks".  I might bring back a collective combo meter as part of a co-op mode, but for now the multiplayer is meant to be competitive.

Other updates:

- menus and other UI improvements
- clouds
- timing and scoring changes