Add transparency to the Spaceman spritesheet
Weapon Selection

At this time I hardcoded numbers 1-6 to be the weapons we currently have
available. you can see that in level.cs. If you click numbers 1-3 you
change your primary weapon, if you click 4-6 you change your secondary
weapon.

I have not done the scroll wheel yet but it should be an easy
implementation. I just wanted to check how everyone wanted it
implemented.

Please let me know if there are any problems
Merge pull request #30 from kalgynirae/andrew_branch2

Weapon Selection
Spawn unicorns on left and right screen sides
Change unicorn sprite angling
Work on unicorn movement
Improve unicorn behavior.

Unicorns now spawn on horizontal level edges, scan vertically for the
player, and charge horizontally. They can now also be eaten by a black
hole.
Merge branch 'improved-unicorn'