Added "excused" vote option type.
Add source links into bill pages.
Merge branch 'master' of github.com:opencivicdata/python-opencivicdata
Merge branch 'master' of github.com:opencivicdata/python-opencivicdata
Added note view on PersonVote object.
Merge branch 'master' of github.com:opencivicdata/python-opencivicdata

Conflicts:
	opencivicdata/models/vote.py