New landing

This commit creates more of brochure like layout for the front page. Here are notes from some of the commits:

- Skip redirect path to API
- Build out the overview page as a splash
- Build out map interactives on the landing to
illustrate higher level ideas to build wit MapBox
- Start putting overview groups into call out sections and
make copy edits
- Piece out sections that are more appropriate to the API docs from the landing.
- Methodize the site.defaultID string replacing
- Formatting, general copy editing
- Vertical spacing to address #542