Create a definitions module with explicit modeling of environment
traversal, moving validation into traversal operations.
Use definitions.
Fix broken test and comment out test case that's intentionally removed.
Add debug logging
Remove commented out and unused test cases
Definitions improvements:
 - Use class factory methods
 - Use @property to lazy evaluate host and roles
 - Name internal function with leading "_"
 - Move examples into doc string
Change comment for future work.
Better logging. Proper handling of components
Move the main task host and role loop into an iterconffiles and call from tasks themselves.
Remove unused initialization.
Update change log and readme per definitions changes.
Document ConfFiles arguments
Fix typo
Use class, not instance
Merge branch 'feature/definitions' into develop

Conflicts:
	confab/conffiles.py
	confab/model.py
	confab/tests/test_generate.py
	confab/tests/test_listing.py
	confab/tests/test_model.py
Simplify conffiles loop.