Robust rule definition

[NithinChintala]

It would be nice to define some more simple rules using just class variables to avoid __init__ logic, i.e. say a rule to Parse

This data is on a single line 5

to

[5]

With a rule like

class MyRule(SplitterRule):
     INDEX = 7
     CONVERTOR = int

could be nice to optionally define the tags (though we need logic to prevent these being defined both at the class and instance level)

class MyRule(Rule):
    START_TAG = "START DATA"
    END_TAG = "END_DATA"

    def process_lines(self, start_line):
         ...

[NithinChintala]

If we add START_TAG and END_TAG class vars we probably will need a new method initState that is simply called at the end of init that can set up any non START_TAG / END_TAG state, this would allows users to not have to re-do the choose the init arg or class arg logic when over-riding initialization