This introduces a very sophisticated algorithm to determine the ordering
of versions on the rendered docs' start page.
(Spoiler alert: It maps "master" and "current" to the largest possible
float values and converts a version like "1.2.3" to "1002003".)
Uses basically the same code as the lint docs page as I didn't want to
reinvent anything: A simple python script (inline in deploy script)
writes an array of versions to a JSON file, which gets turned into a
list of links using a bit of angular.js code.
Fixes#1917
