Documentation tweaks
move 'group_by' to all_stances

How to group the output should be selected at the time of generating
the stances, not when instantiating the Stancer.
Add pointer to separate indicators

Add a _comment field in issues.json to note that the indicators for
Issue 2 are in a separate file.
No need to include votes.json in tests

test_options and test_remote don’t use the separate votes.json data, so
don’t include it.
Add a third test voter
remove needless use of 'colorize'
Bump version

The change to how group_by works should really get a version bump.
remove needless use of 'json'
Remove documentation about People data

Trying to (for example) work out what Party Group an MP was in at the
time of a vote is out of scope for Stancer (at least for now). Anything
that someone might want to group by should be pre-processed into the
vote records before passing to Stancer.