Added endgame_conditions to Game class, and a check before each turn to see if the player achieved them.

This means that the endgame conditions are universal for all maps. This may eventually be moved into the map definition itself, but for now this is less complicated.

We also need a better endgame message, it is quite dissappointing to win right now.

Fixes #84.
Merge pull request #90 from ChodeGames/endgame

Added endgame conditions