Mmf-setup

- Use python3 for CoCalc setup. (Is a problem on Docker images).
- Ignore matplotlib errors.

- Resolves issue 28: Failure of `mmf_initial_setup` on Mac OS X if .DS_Store files exist.
- Resolves issue 29: Relative paths in config files resolve to absolute paths
- Added aliases `findpy`, `findf`, `finda` etc. for CoCalc for running `find` + `grep`.

- Resolves issue 26: Significant improvements for installation on CoCalc.
- Moves `~/.bashrc` to `~/.bashrc_cocalc` so we can insert `~/.local/bin` to the
`PATH` for non-login shells. This is important when trying to push with `hg` over
SSH, which runs `hg` without logging in. Our new workflow needs that `hg` to have
access to `evolve` etc. Previously this worked by updating these with the system
`Python 2` version of `hg`, but that now fails with new projects, so we have removed
this.
- Add `.hgrc` tweaks to top-level cocalc `~.hgrc` (might as well include `hgrc.lga`
here now so students etc. can see these. Don't enable `evolve` etc. by default
though.)
- Users should now call `eval "$(mmf_setup -v -H)"` rather than using source
`. mmf_setup -H`. Sourcing `mmf_setup` now emits a deprecation warning message.
- Cocalc install is now tested in an isolated manner. (Only the `nox -s test_cocalc`
works... see issue 27.)
- Make `hgrc.full` POSIX compliant (work with `sh`). (Was causing GitHub workflow to
fail.) Scripts still require `bash` which is explicitly chosen when we call
`run-tests.py`.
- Working GitHub workflows and cocalc tests.
- Updated release process.

- Make `mmf_setup -v` output clean so that we can `eval "$(mmf_setup -v)"` rather than
sourcing. *In the future we will make this a python file, so `eval` will be the only
option.*
- Fixed issues with `nbinit()` failing with not paths defined.
- Added more tests.

- Resolves issue 23: Drop support of nbclean mercurial extension (to hard to
maintain), thereby making issues 1, 3, 8, 9, 11, obsolete.
- Remove installation of old obsolete notebook extensions like Calico tools,
[RISE](https://rise.readthedocs.io/en/stable/installation.html) etc. These can all be
installed now with either the standard extensions, or pip.
* With pip:

bash
python -m pip install jupyter_contrib_nbextensions RISE
jupyter contrib nbextension install --user


* With conda:

bash
conda install -c conda-forge jupyter_contrib_nbextensions rise
jupyter contrib nbextension install --user

See also
[NBExtensions](https://github.com/ipython-contrib/jupyter_contrib_nbextensions).

- Improved test isolation.
- Expanded options for `mmf_setup`.
- Mercurial configuration is now in two stages: `hgrc.lga` which gives the `hg lg`
command safely using only builtin modules, and `hgrc.full` which includes this,
and also activates the `hg-git` and `evolve` extensions. This also applies the
`update` hook for including `.hgrc` files, but asks the user for confirmation
because this is a security risk.

- Added `mmf_setup cocalc` initialization for CoCalc.com projects
(changed from `mmf_setup smc`).
- Add message to `nbinit()` call indicating that HGROOT has been added
to `sys.path`.
- Resolves issue 22 with git username classes on CoCalc.