Add --random_selfplay option to play 1 game with random agents, which

[rozim]

shows a bug - the moves made ("Player XXX played MOVE") always
have increasing indices.

Sample output:

python -u main.py --random_selfplay
...

Player o rolled <6, 4>.
Player o played** ((16, 20), (0, 6))**                                              <-- note increasing indices
| 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 |
| -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- |
|  x |    |    |    |  o |    |  o |    |  o |    |    |  x |
|  x |    |    |    |  o |    |  o |    |    |    |    |  x |
|  x |    |    |    |    |    |  o |    |    |    |    |    |
|  x |    |    |    |    |    |  o |    |    |    |    |    |
|  x |    |    |    |    |    |  o |    |    |    |    |    |


|  o |    |    |    |    |    |  x |    |    |    |    |    |
|  o |    |    |    |    |    |  x |    |    |    |    |    |
|  o |    |    |    |  x |    |  x |    |    |    |    |    |
|  o |    |    |    |  x |    |  x |    |    |    |    |    |
|  o |    |    |    |  x |  o |  x |    |    |    |    |  o |
| -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| 11 | 10 |  9 |  8 |  7 |  6 |  5 |  4 |  3 |  2 |  1 |  0 |
<Player x>  Off Board :     Bar :
<Player o>  Off Board :     Bar :
Player x rolled <5, 1>.
Player x played **((7, 8), (8, 13))**                <-- this player also has increasing indices
...

[jimfleming]

Thanks for the PR! I think this is correct (per your email) but I'll need to test it. I'll try to review and test before the end of the week.