swap_players documentation improvement
WhosTurnGenerator slight refactoring

made explicit use of swap players to clarify control flow
additional documentation to WhosTurnGenerated

clarification for the slightly counterintuitive __init__ function
standardized gen_play_permutations documentation

now using " -- input_parameter: description" form
also added a bit more clarification
Node now tracks child computer_wins and human_wins

This enables the ai to compare paths looking for the ones with
the best ratio of computer_wins to human_wins
add_nodes_recursively documentation improvments
recursion now sums both computer and human wins

previously, only potential computer wins were summed. Now that both
potention computer wins and potential human wins are summed, it's
possible to make a comparison between them, which should enable
the ai to be better later on
add_nodes_recursively: some assert statements

making sure that player_turn and computer_player both are either
1 or 2
build_decision_tree documentation fix

I had incorrectly documented that passing a depth of 0 to
build_decision_tree does not limit recursion. It actually stops
recursion immediately. Fixed documenation to note this.
added a bit of board testing code to main