correction in init method of RuleCPD. Earlier it was setting the value of rules to None instead of empty dict when no argument was given
adds method to verify the rules given by user in init and add_rules methods [refs #140]
Minor correction in docstring and adds a TODO
more efficient _verify method. Replaced two loops with itertools.combinations and fixed return statement (Earlier was returning just True due to which other function (init and add_rules) trying to access the 0th index of the returned value were throwing error.
tests for RuleCPD class
Merge pull request #157 from ankurankan/dev

Implementation of RuleCPD and tests