better titles
better meta descriptions
use post 'summary' if available; if not, fall back to site.description
use post categories for meta keywords if available
Merge pull request #58 from aminb/enhance-head

'head' Enhancements
add trailing slash to nav and pagination links
Whitespace.
Merge pull request #61 from johnotander/grab-trailing-slash-from-aminb

Cherry pick aminb trailing slash commit. Closes #60.
Attempt to fix site nav positioning.
Fix weird nav alignment issue. Closes #62.
Add some gist styling for embedded github gists.
Override gist syntax highlighting.
Add 404 page, closes #63.
Merge branch 'master' into gh-pages