First commit of incomplete path.py.
More work on MrsPaths.
More changes for the MrsPath branch. Still not completely working.
Generate simple MrsPaths.
Merge branch 'master' into MrsPath

Conflicts:
	delphin/mrs/xmrs.py
Style (PEP8) updates only.
Sweeping changes throughout.

Xmrs now has internal EPs (rather than decomposed structures),
and (seemingly) all functions have been updated to match. The
DMRX and MRX codecs have been fixed so they both read and write,
and the loads() functions now work for both (at least in my tests).
More testing is needed, but the code looks to be in good shape.
Small changes for args, exceptions, and itsdb.

Args are now better at being given the proper argtype at MRS creation.

Exceptions are (partially) in a hierarchy (see issue #16)

The itsdb module can now read .gz tables in profiles.

Also Hook now has a __repr__() method.