Automate conda version by extracting it from setup.py

[maxbriel]

Extracts the versioneer version using conda's build in function to add it inside meta.yaml.
I wasn't able to test properly, because my local conda build fails (also without this change).

See here for an example: https://docs.conda.io/projects/conda-build/en/stable/resources/define-metadata.html#loading-data-from-other-files

[sgossage]

@maxbriel, how do we update the project version with this approach? Is the idea that we'd edit

setup(
    name=DISTNAME,
    provides=[PACKAGENAME],
    version=__version__,
    ...

in setup.py so that version = NEW_VERSION?

[maxbriel]

This branch still has versioneer.py installed, so it will use the github tag of the release to set the version in setup.py. Then the load_setup_py_data from conda loads in the setup.py with the associated variables. This contains the version set by versioneer.py. It then uses that tag to set the conda tag. #784 would replace this with a different mechanism to achieve the same using setuptools-scm.

It should be possible to test this on Linux with conda build.
There it should be possible to verify the tag (I will try to get my local github actions working again).

This basically removes the manual step of updating the conda version number for each release.