adding a page describing the libraries

[davewhiteland]

For now, this is really most useful re: the everypolitician gem.

I've added Python examples too, but until we're ported everypolitician-popolo this is less useful.

My logic in having the duplicated Ruby/Python is that this is simplest; later we can collapse this intelligently in the browser with JS to allow language-based context in the single text. But as that doesn't exist yet, I propose it's better to duplicate.

[chrismytton]

Rebased onto gh-pages.

[chrismytton]

Rebased again onto latest gh-pages, hopefully this time the tests will be fixed!

[chrismytton]

Looks like this is failing because External link http://docs.everypolitician.org/libraries.html failed: 404 No error, which makes sense since that page won't exist until this pull request is merged. So to fix this we need to either tell the external link checker to ignore docs.everypolitician.org, or we need to make html-proofer detect these links as internal rather than external.

[tmtmtmtm]

I've extracted the first part of this out as #33 — there's no need to hold that up behind tweaks to the libraries.html page

[tmtmtmtm]

I tried to rebase this over #33, but it dropped the key commit, so I reverted the earlier revert, which leaves the history a little odd, but with all the files intact again.