Mmf-setup

- Support python 3 - drop support for python 2.
- Conda installable from mforbes channel on anaconda cloud.
- Add missing default.tex theme so that nbinit() brings in math definitions even if no
theme is specified.
- Fixed KeyError: `asyncio` error on failed IPython import.

- Incomplete version... everything here is rolled into 0.3.0

- Made `mmf_initial_setup` python 3 compliant.
- Added logging to `nbinit()` and made some slight tweaks to `HGROOT`.
- Added `\D`, `\sn`, `\cn`, `\dn` commands for MathJaX.

- Resolve issue 20:
- `mmf_setup.set_path.set_path_from_file` allows for configuration of path in
`setup.cfg` file.
- Fix python 3 bug: TypeError: Can't mix strings and bytes in path components

- Added better backwards compatibility for previous changes.
- Simplified nbinit theme management and use `'default'` theme as default.
- New themes only need to overwrite what they need.
- Don't change fonts as default since this does not work well on CoCalc (the code
cells change size on clicking which is a pain.)

- Resolve issues:
- \17: store `mmf_setup.HGROOT`
- \18: safer exception handling with `nbclean` commands so data is not lost
- \19: `nbclean` works with new mercurial API

- Added `\erfi`, `\sech`, `\Braket`
- `import mmf_setup.set_path.hgroot` will add `HGROOT` to path without IPython
- Added standalone `nbinit.py` for use without `mmf_setup` installs.