Example page edits

This is a big commit that touched on all the mapbox.js examples:

- [Titles and description edits](https://github.com/mapbox/mapbox.js/issues/690).
- Code comments along with capitalization and periods of existing ones.
- Sentence case titles.
- Some cleaner formatting around the examples layout
- CSS rework on custom UI controls + formatting.
- Inline links to code documentation now use {{site.mapboxjs}} and not a fixed version key.
- Update language around markerLayer vs featureLayer in inline code comments.
- Use a more diverse set of example baslayers
- Section creation for TileMill interactivity
- Section creation for Features
- One [deletion](https://github.com/mapbox/mapbox.js/commit/46e74490710e6015cf8fc6fe9bd06e8bf3071304) and redirect.