* Allow plugins to add custom command line flags. Addresses #301
* Reduce dependency over Flags class. This will be deprecated so that adhoc flags can be added without any additional manual configuration
* Fix: Argument 1 to "mock_default_args" of "TestMain" has incompatible type "Namespace"; expected "Mock"
* Reduce Flags class to just the initializer.
* Store list of action dest in FlagParser
Abhinav Singh