Add (sub-optimal) support for generic proprietary sentences. This means we can easily skip any proprietary sentences without causing the parser to barf. The implementation is sub-optimal because I prioritised minimising the changes to the existing `parse` routine.

Conflicts:
	pynmea2/test/test_types.py
Re-add test accidentally removed during cherry-pick.
Change the wording of this comment to remove "tuple" because with the changes in master `data` is now a list.
Merge branch 'add-generic-proprietary-sentence-support' into add-xdr-sentence-support

Conflicts:
	pynmea2/test/test_types.py