Magic-wormhole

* Fix `python -m wormhole` on py2. (315)

Thanks to Marius Gedminas, FreddieHo, and Jakub Wilk for patches and bug
reports in this release.

* Python-3.7 compatibility was fixed. (306)
* Support for Python-3.4 on Windows has been dropped. py3.4 is still
supported on unix-like operating systems.
* The client version is now sent to the mailbox server for each connection. I
strive to have the client share as little information as possible, but I
think this will help me improve the protocol by giving me a better idea of
client-upgrade adoption rates. (293)

Packaging changes:

* We removed the Rendezvous Server (now named the "Mailbox Server") out to a
separate package and repository named `magic-wormhole-mailbox-server`. We
still import it for tests. Use `pip install magic-wormhole-mailbox-server`
to run your own server. (240)
* The code is now formatted to be PEP8 compliant. (296)
* The Dockerfile was removed: after the Mailbox Server was moved out, I don't
think it was relevant. (295)

Thanks to Andreas `Baeumla` Bäuml, Marius `mgedmin` Gedminas, Ofek `ofek`
Lev, Thomas `ThomasWaldmann` Waldmann, and Vasudev `copyninja` Kamath for
patches and bug reports in this release.

* Upgrade to newer python-spake2, to improve startup speed by not computing
blinding factors for unused parameter sets. On a Raspberry Pi 3, this
reduces "wormhole --version" time from ~19s to 7s.
* Fix a concurrency bug that could cause a crash if the server responded too
quickly. (280)

Minor client changes:

* accept `$WORMHOLE_RELAY_URL` and `$WORMHOLE_TRANSIT_HELPER` environment
variables, in addition to command-line arguments (256)
* fix --tor-control-port=, which was completely broken before. If you use
--tor but not --tor-control-port=, we'll try the default control ports
before falling back to the default SOCKS port (252)
* fix more directory-separator pathname problems, especially for
bash-on-windows (251)
* change `send` output format to make copy-paste easier (266, 267)

We also moved the docs to readthedocs
(https://magic-wormhole.readthedocs.io/), rather than pointing folks at the
GitHub rendered markdown files. This should encourage us to write more
instructional text in the future.

Finally, we removed the Transit Relay server code from the `magic-wormhole`
package and repository. It now lives in a separate repository named
`magic-wormhole-transit-relay`, and we only import it for tests. If you'd
like to run a transit relay, you'll want to use `pip install
magic-wormhole-transit-relay`.

Thanks to meejah, Jonathan "jml" Lange, Alex Gaynor, David "dharrigan"
Harrigan, and Jaye "jtdoepke" Doepke, for patches and bug reports in this
release.

Minor client changes:

* `wormhole help` should behave like `wormhole --help` (61)
* accept unicode pathnames (although bugs likely remain) (223)
* reject invalid codes (with space, or non-numeric prefix) at entry (212)
* docs improvements (225, 249)

Server changes:

* `wormhole-server start` adds `--relay-database-path` and
`--stats-json-path` (186)
* accept `--websocket-protocol-option=` (196, 197)
* increase RLIMIT_NOFILE to allow more simultaneous client connections (238)
* "crowded" mailboxes now deliver an error to clients, so they should give up
instead of reconnecting (211)
* construct relay DB more safely (189)

In addition, the snapcraft packaging was updated (202), and `setup.py` now
properly marks the dependency on `attrs` (248).

Thanks to cclauss, Buckaroo9, JP Calderone, Pablo Oliveira, Leo Arias, Johan
Lindskogen, lanzelot1989, CottonEaster, Chandan Rai, Jaakko Luttinen, Alex
Gaynor, and Quentin Hibon for patches and bug reports fixed in this release.

WebSocket connection errors are now reported properly. Previous versions
crashed with an unhelpful `automat._core.NoTransition` exception when
the TCP connection was established but WebSocket negotiation could not
complete (e.g. the URL path was incorrect and the server reported a 404,
or we connected to an SMTP or other non-HTTP server). (180)

The unit test suite should now pass: a CLI-version advertisement issue
caused the 0.10.1 release tests to fail.

Thanks to Fabien "fdev31" Devaux for bug reports addressed in this
release.