Use explicit Unicode strings with format

It looks like "%s" % unicode_str automatically converts the
former from an bytestring to unicode

"{}".format(unicode_str) on the other hand, does not
(recall you're just invoking a method on the string object).
You need to explicitly provide a unicode string for the template
instead.

I miss Haskell.
stac-learning addressee: guess EDU addressees
Tidy up educe.stac.lexicon.wordclass

pep8 and pylint
addressee module docs
educe.stac.learning: fix typo-induced regression
Refactor STAC lexicon code

This is one of those refactors that makes everything longer, but
hopefully a bit clearer.
Merge branch 'master' into rst-feat-extract

Conflicts:
	educe/learning/keys.py