shell wrapper meson

[noDGodiaev]

Do we actually need a shell script?

before #29, it made sense. Playing with flags etc. Now it contains only 2 lines of build code and export PYTHONPATH.
Check noDGodiaev#1 for details.

The main question: for what purposes this script will be used?

1. For developers: building package with one line - than the solution is done
2. For CI dev tests to make them cleaner. I checked this:
   export PYTHONPATH inside script doesn't affect on run cell. (some Github Actions magic)
   So the solution: pytest cell can be moved into scripts.
3. If @ev-br have any ideas, I can add them and check them.

That's my solution for now.

meson setup builddir --prefix=$PWD/installdir
meson install -C builddir
# Get python version for PYHTONPATH
ver=$(python -V 2>&1 | sed 's/.* \([0-9]\).\([0-9]\).*/\1.\2/')
export PYTHONPATH=$PWD/installdir/lib/python$ver/site-packages/
pytest mc_lib -v --pyargs

[ev-br]

It's definitely the first one. No need to keep fighting the gh actions. Some sort of script is certainly useful, even if only a convenience record for on-and-off users.

[ev-br]

Having mulled it over a bit, I think we should now merge in your current version. Mostly for documentation for the library --- the main usage is downstream, so we'll iterate based on that.

[ev-br]

all done: gh-41 is merged, README is updated in 6dfae32