FEAT: Add option to supply a random seed (issue #153)

[QBatista]

Adds a random_state option to the remaining files mentioned in issue #153. I haven't added a test for lqnash.py yet -- @cc7768 did you have something in mind to add to this file?

Close #153

[coveralls]

Coverage increased (+0.04%) to 93.704% when pulling 23044a4 on QBatista:add_random_state into f48e7d7 on QuantEcon:master.

[oyamad]

@QBatista Thanks.

• The first line of the docstring of random_state should be

  random_state : int or np.random.RandomState, optional
  

  (See Option to supply a random seed #153 (comment), Option to supply a random seed #153 (comment).)

[coveralls]

Coverage increased (+0.8%) to 94.413% when pulling 7fcf49d on QBatista:add_random_state into f48e7d7 on QuantEcon:master.

[coveralls]

Coverage increased (+0.02%) to 94.395% when pulling 0ab8e24 on QBatista:add_random_state into 21c1a94 on QuantEcon:master.

[mmcky]

Thanks @QBatista this is looking good. I will leave this PR open a couple of days in case others wish to review / comment.