.travis.yml & requirements.txt: Enable travis for documentation.
contribute/translate.rst: fix title underline
.travis.yml & requirements.txt: some fixes

* Install Limnoria.
* Don't specify Python version.
    * I am curious if this is possible.
.travis.yml: use sudo
requirements.txt: remove "pip install"...
.travis.yml: run scripts that shouldn't be used

But the notice about not using them was removed anyay.
Revert ".travis.yml: run scripts that shouldn't be used"

This reverts commit 4c092d493517bac0e56e1b4ed13677491d0180d7.
develop/index.rst: remove ircdb.rst

from library reference. It doesn't appear in generated documentation and
makes the builds to fail.
use/index.rst: remove reference to nonexistant ...

...document "use/plugins/index".
.travis.yml: install requirements from testing

because we are installing Limnoria from testing.

This shouldn't affect the build, so

[SKIP CI]
.travis.yml: update RTFD.
.travis.yml: disable Sphinx errorring

until documentation is fixed.
Merge pull request #8 from Mkaysi/travis

[HELP WANTED!] Test documentation with travis.