add miniver which defines a __version__ based on a tag

[basnijholt]

Makes the current version (at 16 commits aget 0.6.0) for example:

(py38) basnijholt-imac  ➜  miflora git:(version)  python -c 'import miflora; print(miflora.__version__)'
0.6.0.dev16+ga3c5af5