Use snowball.js for stemming.

Stemming is the process of removing suffixes from words to get the 'stem' when
for instance matching words. This allows us to map all different versions of
e.g. socialdemokraterna (socialdemokraternas, socialdemokratisk, socialdemokrat, ...) with one rule.
Add 'term' when creating boost tags.

Add a way to match other words than the tag itself to a tag. For instance we
can match '(s)' to 'socialdemokraterna'.