bloc_aggregates and weighted_aggregates
rewrite Stancer

all about blocs
generate all Issue stances per Party
Tests for party never voting on an issue

Still need to work out what to do to create a zero result
score()

Add method to look up a specific score, rather than indexing into an
array. This lets us not have to explicitly ask for the nil version.
Handle not having voting for an issue

I don’t like how this was done, but it’ll do for now.
generate MP stances

Some issues are too big to fetch in one go (Mongo restricts grouping
size), so get them party by party.
handle failure in mp_stances

group() can't handle more than 20000 unique keys, which is an issue
sometimes
Pull newest lib/stancer.rb from gh-pages branch
Merge branch 'master' of https://github.com/tmtmtmtm/stancer