Implement suggested corrections

[peiva-git]

Is your feature request related to a problem? Please describe.
Some design enhancements could be made

Describe the solution you'd like

1. Get rid of the primitive obsession code smell related to the Piece's and Player's Color
2. Tests refactoring: some tests could be refactored, for example by separating the cases where an Exception is thrown from those where it's not
3. The FreedomLine class could be refactored, especially the is[Direction]() set of private methods: I don't remember how tho @manuelkoso