Docs fixes, docs generation emit no more errors or warnings

* Excluding tests dirs from apidoc generation
* There was a parse error in `utils.log.format_marker`, reworded to avoid it
* Moved the pytest.sel namespace def into fixtures, so you don't have to import
  pytest_selenium in order to not have to import pytest_selenium (derp)
* While I was in pytest_selenium, fixed the `sleep = time.sleep` thing
Register Tree objects with fill singledispatch