Auto-escalate unmount-chroot if -y was passed or 'a' was specified.
Enter, unmount, and delete encrypted chroots.
Pull out mounting encrypted chroots into its own command.

The new command mount-chroot can also create encrypted directories and migrate
existing chroots.
Change mount-chroot's -m to -e and make it not imply -n.
mount-chroot no longer assumes encryption and doesn't soft-fail.
Add support for creating encrypted chroots.
Hide the unmount chroot call in the installer.
Fix unmount-chroot printing to stdout.
Add encryption to the README and USAGE texts.