upgrade Aspen to 0.32
Here's a first pass at upgrading to Aspen 0.32

I went with gunicorn for a web server, because it is much simpler to
configure than uwsgi. Note that this Makefile requires a patched version
of Honcho. I made a PR but I don't know if it will be accepted:

https://github.com/nickstenning/honcho/pull/71
I'm adding a file!
remove our temporary copy of to_rfc822()
Use new json_dump renderer in error.spt
Reformat JSON simplates

With this newer version of Aspen we no longer have special-cased JSON
simplates. Instead they are now regular rendered/negotiated simplates
that utilize a json_dump renderer.
Test and upgrade api-key.json
Test and upgrade the members/index.json endpoint
Test and upgrade about/paydays.json endpoint
Test and upgrade tip-distribution.json endpoint
Upgrade to our forked version of Honcho

See https://github.com/nickstenning/honcho/pull/71.
Upgrade honcho

This version fixes a bug where we couldn't just do `honcho run -e
foo.env py.test`.
Quit working around a Cheroot bug

We're not using Cheroot anymore.
Down to two failing tests

This requires Aspen HEAD, which I didn't vendor yet. I'm waiting for an
0.33 release.
Merge branch 'master' into aspen-0.32
Fix implicit unicode casts; upgrade to Aspen 0.33
Fix bugs around api key

With a staticmethod for _generate_api_key I was seeing weird
interactions across the test suite. Rather than track that down I'm just
punting and making it a normal method.
remove leftover file
remove trailing space
fix Procfile