0.7 release

Release checklist:

- [x] merge storage drivers (#2609)
- [x] merge new random names collection (#2837)
- [x] add install docs for Fedora --> @jamtur01 
- [x] Update Gentoo install docs (aufs is no longer a hard requirement) --> @tianon
- [x] Update Ubuntu install docs (aufs is no longer a hard requirement)
- [x] update information about kernel requirements (there are less). Included in #2609.
- [x] fix checksum error on push
- [ ] release announcement --> @shykes
- [x] green light from @tianon for distro packagers --> @tianon
- [x] Dynamic binary hash issues on update (#2765 #2854) --> @vieux
- [x] Change integration tests to always use the vfs driver (#2862). --> @shykes
- [x] Fix randomly failing TestChangesDirsMutated --> @crosbymichael 
- ~~[ ] Fix engine regressions (#2826)  --> @shykes~~ *This needs to be fixed, but it's already present in the latest stable release, so it's not mandatory for 0.7.0 to fix it. Let's make this 0.7.1*
- ~~Include experimental btrfs driver~~  *This is not necessary for 0.7.*
- ~~Remove temporary hacks (engine/hack.go)~~ *This is not necessary for 0.7. hack.go is there to allow for temporary refactoring. It's a hack from the point of view of the new API. But it's stable and tested nonetheless.*
- ~~Freeze Attach default behavior (#2845)~~ This issue needs to be settled, but we have nothing to gain by rushing it, and even if we wanted there is not enough time to do it tonight