docs: Use 'None' and explain why.

An example should always show the 'best' or recommended usage, not a
possible one and then in a note document the preferred usage.
docs: Add a trick for supplying partial config.

I had to figure this out myself but it's been an incredibly useful
snippet to minimise the amount of configuration a user needs to do. This
is mostly useful for plugins that have more than a few configuration
options.
docs: Update instructions on testing a plugin:

  * Goodbye unittest, hello py.test:
    * Goodbye horrible `setUp` tasks and other bloat
    * Hello pretty `assert` statements
    * Remove other unittest code bloat
    * Change the command invocation for the tests to `py.test`
    * Use `pytest-pep8` plugin for PEP8 support
    * Start the classes with Test to adhere to Python test discovery
      rules
  * Update the .travis.yaml sample:
    * Yapsy fixed their name, so pypi and setuptools are happy now
    * Add testing on Python 2.7 and Python 3.4
  * Add explicit `.. code-block:: python` everywhere. This causes IDE's
    to turn on syntax highlighting for those sections and is more in
    line with the rest of the documentation.
docs: Fix two small typo's.
docs: Add a way to reset configuration.

This is needed when using the partial configuration method so that
people can easily reset a plugin to its default settings.
Merge pull request #276 from daenney/docs-updates

Docs updates
Bump version checker to 2.1.0
Docs: Explain raw webhooks
Preliminary support for TOX network

TOX is a decentralized, anonymous and encrypted chat network.

So far you can with this backend :
invite the bot
1 to 1 chat with the bot
invite the bot to a groupchat
chat in the room with the bot

At this point : no security (anybody can invite the bot)
Pass on TOX backend

- now the basic security is done (admin / not admin).
- message splitting too
- bootstrapping is configurable
Test regression on self.jid
made pep8 happy
Merge pull request #277 from gbin/tox

Support for TOX network
Corrected a regression in xmpp
Presence works in tox
Hooked up the presence events from XMPP
Test & document setting custom headers/status codes in webhooks
Docs: Explain how to use templates with self.send()
Docs: Don't generate apidoc for tox backend for now

It's quite a pain to build it, don't want to scare away potential
contributors by making it difficult to get the necessary dependencies to
build the docs
Added presence to the test backend