Use poetry version command to bump package version

[philipschoemig]

Instead of using an external tool like bump2version the poetry command version could be used to increase the package version. For this to work the duplicate version information in src/bertlv/init.py and docs/conf.py must be removed.

init.py

The version variable could be assigned to the package version retrieved from importlib.metadata.version() as suggested in poetry issue #144. Example code:

try:
    import importlib.metadata as importlib_metadata
except ModuleNotFoundError:
    import importlib_metadata

__version__ = importlib_metadata.version(__name__)

See the complete solution in this comment: python-poetry/poetry#2366 (comment)

However, for python version <3.8 this would introduce a dependency to importlib_metadata.

conf.py

The version should be retrieved by accessing the __version__ variable from the bertlv module. Example code:

import bertlv
version = bertlv.__version__