This makes it easier (possible?) to generate sshuttle.8 from sshuttle.md on
MacOS. We also import the git-enhanced version numbering magic so the
generated manpage can have a real version number.
Including a copy of minimal/do as 'do' in the top directory. To build, just
run './do' or 'make'.
This also builds the ui-macos directory automatically if you're on MacOS.