Add abstraction to the rez file and directory structure through use of "resources": files and folders that are registered with a path pattern, and can thereafter be iterated over by higher level code without knowledge of the underlying structure.
Add a test for versionless packages (i.e. {name}/package.yaml), and fix a bug that it revealed. (yay, tests!)
Use the RezMemCache in the ResourceIterator.  Get timestamps working again.
Fix a few remaining bugs from the resources refactor.
rename rez_config to resources to reflect broader purpose.