Implement a new command-line parser, based on CLI11.
It's a bit more C++'ish, and allows for a lot of fancy things... some of
which we have implemented here.
Update the various commands to use the new Options struct
Remove the old help strings; instead e.g. `mu help view` opens the
manpage.
Integrate the guile scripts more tightly.
Dirk-Jan C. Binnema