emacs_mode indetation
Removed comments from tests. Now all the tests are running.
There are internal tests for the board module since it tests internal
functions.
Trying to add types and spec to the board

@gabrielelana: what do you think about them?
If the position() type is a good idea maybe it should be good to change
the move signature to pass a position() instead of the Row and the
Column.
I have also updated the check/1 so that we are not tied to 'x' or 'o'
atoms but here I have another doubt. Looking at the symbol() type, the
atom 'none' is a valid symbol() so that I would like to enforce this but
I don't know how in this moment.