MNT : simplified ColSpec

was going through gyrations to unpack *args, **kwargs, that is
dumb, just use correctly named positional arguments on the input
MNT : cleaned up DataMuggler internals a bit

 - removed one dictionary
 - keep track of column specs as ColSpec objects
ENH : add recreate_columns method

Completely resets the brain of the data muggler to use a different
set of columns.

Emits the new names on new_columns signal.
Merge pull request #2 from tacaswell/csx_comm

Csx comm