See tests/data/test.vcf.gz and
<https://github.com/brentp/cyvcf2/issues/304>.

Currently, the "AO" counts are the sum of alt counts.
A more detailed report is more complicated to implement.

This reverts commit 829e0265.

Automatic version from git tags using setuptools-scm

See https://setuptools.pypa.io/en/latest/userguide/pyproject_config.html
and https://github.com/pypa/setuptools_scm/

Also adopting src-layout.