Improve and test history API

[donbonifacio]

The text serializer (#27) introduced the history concept. Each time a turn is processed, the raw turn actions will be stored in a :history key on the game.

We need a proper API on the game for handling the history, and also unit tests. We need:

• Get the history from the game
• Register turn actions
• Write unit tests
• Given a game, get the game on a specific state: beginning, end, turn X