Adding cascading options

This feature adds cascading options (similar to how css cascades) for
player_config options.  This is desirable for situations where users would 
want different configuration options for different experiments.  The changes 
are listed under Configuration in README.rdoc.

Changed files:

Gemfile: adds mocha for mocking in unit tests (not needed for deployment)

Rakefile: adds test_cascading_options and test_all tasks

experiment.rb: adds a readable options hash (to be edited, but not set)

epsilon_greedy.rb: takes advantage of BasePlayer#get_option for :epsilon

softmax.rb: takes advantage of BasePlayer#get_option for :temperature

generators/bandit/templates/bandit.rb: makes the yml hash a
HashWithIndifferentAccess so it can be accessed with strings or symbols

test/cascading_options_test.rb: unit tests for cascading options

test/helper.rb: including mocha