Use plugin to populate __version__

[willmcgugan]

So tired of issues asking about __version__. This plugin should solve it once and for all, while allowing us to keep the same work-flow.

https://github.com/tiangolo/poetry-version-plugin

[olivierphi]

It turns out that the plugin itself is in alpha version at the moment, and relies on a beta version of Poetry 1.2.x - so we'd better wait for these 2 tools to be released in proper versions before using them :slightly_smiling_face:

[bjourne]

+1 for adding __version__. Would make it easier to write good bug reports.