README.md: add Limnoria's requirements.

They have common requirements between this repository and even stock Supybot/gribble.
Merge pull request #208 from Mkaysi/patch-1

README.md: add Limnoria's requirements.
IgnoreNonVoice: Add plugin.
IgnoreNonVoice: Add config variable enableIfModerated.
IgnoreNonVoice: Also ignore invalid commands.
IgnoreNonVoice: check if message is received on channel. Closes GH-213.
.travis.yml: enable fast finishing

As with Limnoria, this sets the build as failed/errorred immediately
when one build fails without having to wait for so long time.

As we noticed with Limnoria, the builds that haven't failed at the time
of one build failing will continue building and this only gives
information about build failing faster.
README.md: add IgnoreNonVoice
IgnoreNonVoice: add README.md

[SKIP CI]
IgnoreNonVoice: Do not ignore in private.
requirements.txt: add pysandbox

Warning: this makes git a requirement when using `pip install -r
requirements.txt`.

Closes #216
.travis.yml: allow pypy to fail

Pypy isn't supported by pysandbox.
.travis.yml: fix email notifications

Closes #218
StdoutCapture: Fix Python 3 support of @pastebin.
IgnoreNonVoice: Fix issue when a command is called with @network command (the channel does not exist on the target network). Closes GH-219.
Variables: add @unset.