Have version in single place of update-able with single command

The pyproject.toml and docs/confi.py both define the version of the package. To make a new release the version has to be updated in both places. It would be nice to have a single place or a single command like [bump2version](https://github.com/c4urself/bump2version)

I would be also be nice to have `run-bmi-server --version` and `from grpcbmi import __version__`.

Side-quest of #130.

Start by comparing the version definitions in pyproject.toml and docs/confi.py, then locate the run-bmi-server entry point and the grpcbmi package. Decide how the version should be maintained and verify that a release updates it once, run-bmi-server --version reports it, and grpcbmi.__version__ exposes it.

Written by the indexing model from the issue text.