Yet another width setting system

I can't believe this worked! Here's the motivation:
* Our masthead jumping around __sucked__. I made it width 10. Now when
we navigate between pages it's *awesome*. Takes some getting used to
for us, but I think it's better.
* In templates, you set the width as an integer and the base template
and some jinja math magic center it and stuff.
* More appropriate width on the start project page
Merge pull request #113 from teslaworksumn/widths

Yet another width setting system
Merge branch 'master' into button-up
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