FlowMod should validate instructions.
Refactor ActionIterator, ActionRange implementations.

ActionIterator is a ProtocolIterator.
ActionRange is a ProtocolRange.
ActionList is now a ProtocolList.
Changes to ofpx decode.

Change ofpx decode to use Subprogram class.
Add support for verify & quiet command line arguments.
Add validateInput() method to InstructionRange.
Refactor ofpx ping as a Subprogram
Improve TableFeatures YAML output for actions.

Implement ActionType conversion to string.