Chapps

- Correcting serious error-handling bug which would cause an
endless, log-filling loop when encountering unexpected
connection errors. All users are recommended to update their
software immediately. This one was a bit sneaky for us; we've
run this software in an intense production environment for
months before finding this defect.

- Correcting/completing `domain flush` functionality in `chapps-cli`

- Ensuring that SDA `allow`/`deny` functionality causes the relevant
cache entry to be deleted in order to ensure it is repopulated when
next accessed.

- Adjusting production syslog message format to preface it with
the processName and PID as with the postfix logs.

- Correcting a couple of bugs in the CLI script, wherein:
- trying to show a nonexistent domain would cause an un-trapped
error
- trying to show a domain's option flags caused an un-trapped
error if the SPF libraries are not installed

- Adding HELO whitelisting option to global CHAPPS config. Right
now, it is only implemented for inbound policies. It would not
be hard to add to outbound ones as well. In such a case, one
might want distinct lists.

- Update the .readthedocs.yaml config file which I had completely
forgotten about. This file contains among other things the
command line for `sphinx-apidoc`, and so it is the proper place
for the exclusion pattern in order to ensure that builds on
readthedocs.io function.

- Implement exclusion pattern in Makefile to cause sphinx-apidoc
to skip Alembic subhierarchy, because part of it throws an error
when loaded during the doc-build and there seems to be no reason
to embed its docs in these.

- Update CHAPPS modules list in its main `__init__.py` to reflect
recent architectural changes.

- Ongoing efforts to get the documentation to compile
automatically at readthedocs.io. Another debug log instance at
module scope needed protection. I think this is the last one
based on some bogussy codebase searches.

- Corrected some old documentation which referred to an obsolete
module called `actions` which became disused several revisions
back.

- Removed `actions` module source file from repo, as it was no
longer used and its old, deprecated code was breaking
documentation auto-building.