Move doc pages into main branch

Moves docs + generation into main branch.

- [ ] @edenh review
- [ ] Merge in to `master`
- [ ] Remove `mb-pages`
- [ ] **PAUSE until all PRs merged**
- [ ] Push `master => mb-pages`
- [ ] Make `mb-pages` default branch
- [ ] Nuke `master`

cc @edenh @mourner @kkaefer @ansis @lbud @jfirebaugh