This adds initial support for an sqlite database that is shared across
multiple tasks of a single SBY file and that can track the status of
individual properties.
The amount of information tracked in the database is currently quite
minimal and depends on the engine and options used. This can be
incrementally extended in the future.
The ways in which the information in the database can be queries is even
more limited for this initial version, consisting of a single '--status'
option which lists all properties and their status.
Move parser generation into a seperate file to avoid import issues with bad python modules during docs gen.
With the requirements.txt provided to readthedocs, there shouldn't need to be any other changes?
Also I've never been able to run `make test` so I'm not actually sure if the changes break sby, but they shouldn't.
