Example

iex> GameOfLife.BoardServer.start_game
:game_started
iex> GameOfLife.BoardServer.start_game
:game_already_running
iex> GameOfLife.BoardServer.stop_game
:game_stoped
iex> GameOfLife.BoardServer.stop_game
:game_not_running
iex> GameOfLife.BoardServer.change_speed(500)
:game_started
iex> GameOfLife.BoardServer.stop_game
:game_stoped

iex> GameOfLife.BoardServer.set_alive_cells([{0, 0}])
[{0, 0}]
iex> GameOfLife.BoardServer.alive_cells
[{0, 0}]
iex> GameOfLife.BoardServer.add_cells([{0, 1}])
[{0, 0}, {0, 1}]
iex> GameOfLife.BoardServer.alive_cells
[{0, 0}, {0, 1}]
iex> GameOfLife.BoardServer.state
{[{0, 0}, {0, 1}], 0}

iex> GameOfLife.BoardServer.generation_counter
0
iex> GameOfLife.BoardServer.tick
:ok
iex> GameOfLife.BoardServer.generation_counter
1
iex> GameOfLife.BoardServer.state
{[], 1}