0.7 release

Release checklist:

- [ ] merge storage drivers (#2609)
- [x] merge new random names collection (#2837)
- [ ] add install docs for Fedora
- [ ] add install docs for other distros
- [ ] update information about kernel requirements (there are less). Included in #2609.
- [x] fix checksum error on push
- [ ] release announcement
- [ ] green light from @tianon for distro packagers
- [ ] Remove temporary hacks (engine/hack.go)
- [ ] Freeze Attach default behavior (#2845)
- [ ] Dynamic binary hash issues on update (#2765)
- [ ] Include btrfs driver