Add a DSC Resource Development/DevX module

[michaeltlombardi]

As a developer and maintainer of DSC Resources, I would like to have a helper toolkit I can leverage during my development process to help ensure a common toolkit is being used and emerging patterns can be incorporated into it effectively.

This may also be a place to put resource-developer-focused improvements and extensions if the PSDesiredStateConfiguration module is to be kept for runtime concerns/the base platform only (which would minimize the amount of code that needs to be shipped to a machine to invoke a DSC Resource).