Feature: lay groundwork for implementing 'player starts game'

by adding `lib/tic_tac_toe/game.rb` and listing required classes
in `lib/tic_tac_toe.rb`

In the future, TicTacToe classes can be added to `lib/tic_tac_toe.rb`
Tests: Add failing cucmber test for 'player starts game'

so we can do BDD.

* Added start game scenario
* Used a test double to capture output. Note: used `def out_put` because `output`
is a private Rspec method in the scope of the step definition
Feature: Player starts game

* Added game class to TicTacToe module

closes #1
Merge branch 'feature/player-starts-game'