upgrade CodeMirror to 2.37. Fixes #96.
basic support for 3-tab odd-numbered questions. Answer and discussion tabs are currently just placeholders
misc tweaks to restore some necessary styling after CodeMirror upgrade
make the Disqus directive a proper docutils node instead of a raw HTML node
Merge branch 'master' of github.com:bnmnetp/runestone
Merge pull request #100 from isaacdontjelindell/master

Upgrade CodeMirror to 2.37.