Share register models

[andig]

Continued from sunspec/models#44:

I have for some time been developing https://github.com/volkszaehler/mbmd - different language, different goals.

One thing that I see as common denominator is the mapping of specific registers (especially outside of sunspec) to a) their physical meaning and b) the necessary en/decoding. If you which we could join forces and design some kind of meta representation that would allow to create the likes of https://github.com/volkszaehler/mbmd/tree/master/meters/rs485 in a generative way.