Generate HTML files for daily tweets.
Added previous and next values to tweet layout.
Use symbols for the top-10 buckets.
design tweaks
Merge branch 'develop' of https://github.com/measuredvoice/shining-sea into develop

Conflicts:
	site/layouts/tweet.html
designing
Added helpers for text display and links.
designing
designing
designing
Replaced "1st most engaging" with "most engaging".
Changed medium to medium-sized.
(Old data needs to be re-summarized to catch the change.)