correcting classifiers
adding add_cleanup_path()
adding configuration_directories(), split_versions(), and load_yaml()
adding test for the default config root
adding configuration_files()
Refactoring code into single class (cleaner inputs and functions).  Need to fix the tests and update the docs.
readding test for top level class
adding tests for the local variables and split version
adding some doc strings
wrong input argument
fixing logic bug for filter_missing
adding tests for directories()
local_dir should not be prefiltered, reforming logic in directories() to mirror files()
fixing tests to account for removal of pre-filtered paths
adding DEFAULT_ prefix to classvars
adding DEFAULT_ prefix to classvars
adding additional instance tests, added test_files_unfiltered()
added remaining tests for file filtering
don't let load error break parsing of other files
don't populate os.environ by default..