Various things

A few things in here:

- New README.
- An about page instead of the press page.
- A page with issues tagged `help wanted`.
- A page with internal guides and tools we've made.
- Blog posts can use `<!--more-->` tag to choose the excerpt shown on the main page (with default to 50 words).
- A bunch of `meta` tags in the HTML.
- An RSS feed, I hope.
- A gem that auto-generates a sitemap.
- Add Twitter, Meetup, etc. to the navbar as icons.
- Fix a bug in navbar collapse for mobile.
- Allow deeplinking on blog posts and such.
- Reorganize files to be a simpler structure.

As a result, this should close #93, #94, #95, #98, #100, and #104.