Split library into multiple files. Create new Ladder base class. Rename URL to URLPath.
Add DelimitedPath class.
Add OSPath class.
Update library api.
Add tests for new classes and split up over multiple files.
PEP8.
Add "clean-files" to the beginning of "test-full".
Revert clean-files change since target only runs once.
Update README and CHANGES with next release features.
Release v0.4.0.