First attempt with minimum features

* Aliens that move and change direction
* Controllable player that can move left and right and shoot
* Collision detection: aliens can be killed
Re-did collisions. Doesn't work dough?
aliens were in the swarm
Adds midje, a testing library
Adds tests proving collisions work

Projectiles which hit the edges of the aliens
also count as a hit
partial apply *magic*
Merge pull request #3 from petterik/collisions-2

Collisions 2