Add formal CAA support to YamlProvider

adds an example of how to setup geodns to the docs

Improve setuptools capabilities

Make PowerDnsBaseProvider's timeout configurable

fix error on version

adding minimal version only for contributors

define 3 kinds of requirements (base, dev, test)
retrieve version from __init__.py
define setuptools minimal version

in CI install full (base, dev, test) dependencies

OVH: Add support of DKIM records

Add support for included and excluded records

Improve Validations for None/Empty values, Ignore None/Empty values during dump

dump does not write invalid value(s) to yaml

Allow enabling lenient on a per-record basis with octodns.lenient

set default value for nsone cname to None, use first value if non-zer…

```
---
'':
    octodns:
        ignored: True
        lenient: True
    type: CNAME # not valid to have a root cname
    value: foo.com.

0.8.8 version bump and changelog

use . instead of source [SC2039]

Add proposed google cloud provider for #23

use uuid4().hex to ensure unique zone_name generation and thereby streamline with the other providers.

Handle Manager.dump with an empty Zone

add ability to configure update/delete thresholds

Cache googleclouds zones so that populate dont have to list all each time called.

* in _rrset_for_X functions, use values instead of data attribute.
* Small typo fixes and removals of redundant steps etc.
* Unset GOOGLE_APPLICATION_CREDENTIALS in coverage script.