Docstrings, typos, small fixes.
Show traceback if CLI throws an error during tests.
Add apply_to_document method to metrics.
Adding @metrics.require decorator.
Add get_id method to metrics. However it's still unused yet.
Restructuring directories. Moving pre-built pagetypes/checks/metrics into its own directory.
Using defined naming conventions for checks.
Add docs and tests to 'make all' command.