Fix some typos, small errors, debug leftovers. Removed unused
mu-cmd-count.cc. Improve test-coverage. Fix manpage.
Make the errors for unknown commands a little friendlier.
Move the various seq_ functions, as well as std::(stable_)sort,
std::accumulate, std::transform, std::find, std::find_if to their C++20
std::ranges counterparts.
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.
Update all cc code using .clang-format; please do so as well for future PRs
etc.; emacs has a handy 'clang-format' mode to make this automatic.
For comparing old changes with git blame, we can disregard this one using
--ignore-rev
(see https://www.moxio.com/blog/43/ignoring-bulk-change-commits-with-git-blame )
