Add new page for lightning talk topics using an embedded gist

[aganders3]

This PR adds a page that lists lightning talk topics, and fixes #4. The topic list is maintained in an embedded gist. Right now that gist is mine (https://gist.github.com/aganders3/5fa64dd9391103b82abc), but feel free to change it. There is a commented line in lightning-talks.rst that will instead embed @godber's gist from the page he made in the comments from issue #4.

[godber]

Looks awesome, I'll try to accept and deploy it tonight.

[wtolson]

:+1: :sparkles: