Added category list to 404 page
Added category lists/page, closes #14
Added CDN-hosted bootstrap.js
Added credit to NetzwergX for Jekyll Template Toolkit
Removed Instapaper "save later" link, closes #12

Removed the link because I couldn't get it to look like I wanted and I
assumed anyone who uses Instapaper/Pocket/etc. will use their own
bookmarklets.