Plugin to create link reference to another post / page inside the site

This plugin adds a new role called :ref: to the rst compiler. Here is
an example of how it works:

    Please, check my :ref:`philosofy-ideas`.

Or, giving the text to link:

    Please, check my other :ref:`post about philosofy <philosofy-ideas>`.
Rename :ref: role to :doc:

This is to be more compatible with other compilers like Sphinx, that
uses :ref: to create a CrossReference and :doc: to link to another
document.
Remove unused import
Always use the correct language (automatically)

It's not needed to use the DEFAULT_LANG config
Warning for twin slugs

If the :doc: role finds more than one post with the same slug, it will
use the first one, emmiting a WARNING.
CHANGES.txt updated with the :doc: role documentation
have reST shut up about those two

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
Revert "have reST shut up about those two"

This reverts commit 9d4779acadf664d8d9f59c21856e7d98642bebfb.
Fix #734
make docs in the sample site fuller so that integration tests don't fail now that manual.txt has a doc reference
merged master
make tests pass
enable the live doc roles
cleanup tests a bit
solve things the wrong way
fix tests more
Make integration tests 4x faster
Merge pull request #730 from getnikola/refrole

Plugin to create link reference to another post / page inside the site