Created a few more enemy designs.

Merge pull request #6 from haroldo-ok/alternate-enemy-sprites

Alternate enemy sprites

Implemented player collision against enemies and their shots.

Merge pull request #5 from haroldo-ok/collision

Implemented player collision against enemies and their shots.

Version 0.3

Implemented enemy behavior for each level.

Version 0.2

Added enemy shots and sound effects.

First release

For now, it just displays the player, one type of enemy and the player shots.