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.