Configsuite

Improvements:
- Update documentation on allow none
- Add section on transferring from `0.5` to `0.6`
- Add release notes section to documentation

New features:
- Allow elements to take `None` as value
- Specify default values in the schema
- Generate documentation from schema

Improvements:
- Python 3.8 support

Deprecated:
- Using `Required` in the schema

Add tests for all code snippets in documentation to test suite.

Documentation fix

Fix typo in documentation example

Feature:
- Support context validation for containers

Improvement:
- Allow for chaining BooleanResults, and hence transformations and validators.