Removed obsolete delphin.mrs.basemrs module.
Changed Lnk to be instantiated with classmethods instead of a single constructor.
Changed Pred to be instantiated with classmethods instead of a single constructor.
Updated MrsVariable with a more robust hash code, changed VarFactory to VarGenerator, and changed some 'h's to HANDLESORT.
Fixed a syntax error in the last commit in delphin.mrs.dmrs.
Added Hook class.

The Hook class contains information like the LTOP and INDEX (and maybe
XARG in the future). It's purpose here is mainly to follow the formal
definitions of MRSs. Properties on Xmrs allow for direct access to
ltop and index.
Make ElementaryPredication not a subtype of Node.

This small change necessitated many changes throughout. Now there are no
longer cv or carg members of ElementaryPredication, and instead there are
properties that retrieve these from the argument list. This made some
serialization/deserialization tasks simpler.

The code is not fully working. In particular, the DMRX serialization is
producing bad links. I'm not sure if DMRX reading is working or not.