Moved the metadata into setup.cfg from setup.py.

DNSSEC refactoring.

make `name in zone` consistent with `zone[name]`

specifically, allow name to be a str, and raise a KeyError if name
cannot be converted into a dns.name.Name

Fixed the dependency on poetry instead of poetry-core in pyproject.toml.
Fetching the version from git tags now when using setuptools (for poetry we cannot do that currently, see https://github.com/python-poetry/poetry/issues/693).

Reorders some of the operations related to RRSIG validation.  The net
effects here are that the code performs all of the parts of validation
that are not specific to the keys first before the parts that are
specific to keys (and need to be repeated for each key).

This also fixes the inconsistency that if there are multiple keys that
match an RRSIG, a single malformed key would lead to an exception, but a
signle failed signature validation would not.  In both cases, an
exception should only be raised if no keys successfully validate the
RRSIG.

doc fix: change fname to name