Vast documentation improvements.
Moving mapping tools to their own module
Bugfix to moved mapping tests
Removing duplicate MutableMappingBase
An abstract base class for a fallback dictionary.
A new ConfigureAction to link config and argparse
Documentation Improvements
New mapping classes: Fallback and Regex
A new .yaml module, for customizing YAML behavior
Minor docs update to .core
Merge branch 'feature/mapping' into develop