Add Player.delete_action, NormalFormGame.delete_action

[oyamad]

Example:

g = gt.NormalFormGame([[(3, 0), (0, 1)], [(0, 0), (3, 1)], [(1, 1), (1, 0)]])
print(g)

2-player NormalFormGame with payoff profile array:
[[[3, 0],  [0, 1]],
 [[0, 0],  [3, 1]],
 [[1, 1],  [1, 0]]]

nums_actions_deleted = np.zeros(g.N)
step = 0
while True:
    for i in range(g.N):
        actions = g.players[i].dominated_actions()
        g = g.delete_action(i, actions)
        if len(actions) > 0:
            step += 1
            print('Step {step}'.format(step=step))
            print(g, '\n')
        nums_actions_deleted[i] = len(actions)
    if nums_actions_deleted.prod() == 0:
        break

Step 1
2-player NormalFormGame with payoff profile array:
[[[3, 0],  [0, 1]],
 [[0, 0],  [3, 1]]] 

Step 2
2-player NormalFormGame with payoff profile array:
[[[0, 1]],
 [[3, 1]]] 

Step 3
2-player NormalFormGame with payoff profile array:
[[[3, 1]]] 

[coveralls]

Coverage increased (+0.03%) to 94.451% when pulling 8703710 on gt_delete into 3bb4d7d on master.

[mmcky]

thanks @oyamad must have missed this one in my review last week. I will merge this now.