Cloud-mappings

* Add a `storage_provider` property to `CloudMapping` to make it easier to access underlying storage directly and/or create different cloudmappings with different prefixes/serialisers.

* Default Azure credential to `None`, fixes 20
* Fix `__contains__` logic when `read_blindly=True`, fixes 21
* Overhaul tests such that each test overlaps less

Version 2 overhauls the cloudmappings API:
* Simpler interface that better highlights the internal docs, allowing IDEs to pick up doc_strings!
* Ability to create multiple mappings based on one storage resource
* Each mapping can have a different prefix in the resource and be isolated at the key level
* Serialisation easier to extend and customise

What's Changed
* Version 2! by JJ11teen in https://github.com/JJ11teen/cloud-mappings/pull/17


**Full Changelog**: https://github.com/JJ11teen/cloud-mappings/compare/v1.2.2...v2.0.0-alpha

What's Changed
* Remove debug print by JJ11teen in https://github.com/JJ11teen/cloud-mappings/pull/16


**Full Changelog**: https://github.com/JJ11teen/cloud-mappings/compare/v1.2.1...v1.2.2

What's Changed
* Wrapper arg fix by JJ11teen in https://github.com/JJ11teen/cloud-mappings/pull/15


**Full Changelog**: https://github.com/JJ11teen/cloud-mappings/compare/v1.2.0...v1.2.1