Footnotes

Squashed commit of the following:

commit 21be7962866399467a5759f372be7f95abecb4ec
Author: Jordan Byron <jordan.byron@gmail.com>
Date:   Sun Feb 2 15:18:46 2014 -0500

    Small style tweaks to footnotes

commit f07f71ef111ffa50c02009f2f1bb6b3f11b0263a
Merge: fdf1f00 78ed049
Author: Jordan Byron <jordan.byron@gmail.com>
Date:   Sun Feb 2 15:08:10 2014 -0500

    Merge branch '209-footnotes-in-markdown' of git://github.com/stephenorr/practicing-ruby-web into stephenorr-209-footnotes-in-markdown

    Conflicts:
    	Gemfile.lock

commit 78ed049f35d83de4bc20dd31073f47a96a8ae150
Author: Stephen Orr <steve@stephenorr.co.uk>
Date:   Sun Feb 2 15:35:27 2014 +0000

    Add integration tests for Markdown footnotes

commit 9843e94741ae3d18c52e35e4cdd4dab1b6fc5a05
Author: Stephen Orr <steve@stephenorr.co.uk>
Date:   Sun Feb 2 15:34:45 2014 +0000

    Add a test helper to verify that the provided CSS is NOT found

commit 92e963f00df9e532e756937125dd6f1231ea664c
Author: Stephen Orr <steve@stephenorr.co.uk>
Date:   Sun Feb 2 14:35:08 2014 +0000

    Update article rendering to support footnotes in Markdown.

    This commit updates the gemfile to use redcarpet from the Git master
    branch, which supports footnote rendering. This should be version
    3.1.0, but this has not yet been tagged.

    Closes #209.