Add Consolas font (in case it’s not present)
Blue world's steps headers
By default, don’t regenerate PDF.

If it looks different to the version in git, then regenerate it. There’s
also a --rebuild switch to override.
Merge pull request #107 from codecleaner/world-pdf-coloring

Blue world's steps headers
Update Gemfile to use the latest Sass
Add a `clean` arg, that cleans the output dir
Update call to autobuild (since args have changed)
Hack to stop updating zips.

If a zip exists, assume its contents are correct.