Adding code for lifting over between sequences and the reference genome.

Provides code for going between a sequence that maps to regions of the reference genome (e.g., a transcript) and a reference genome position, and vice versa.
Oh wait, no, don't do this -- this is the UCSC-style of "if the coordinates are in descending order, then it's on the negative strand" region.  But this is the source of additional complication and subtle bugs with region coding later on!  I'd argue for a ``ReferenceRegionWithOrientation`` implementation that's isomorphic to the ``ReferencePositionWithOrientation`` implementation, with start/end coordinates that are always ascending and an explicit boolean that handles whether the strand is positive or negative.