Remove detailed list of attributes from ``using`` page now that they are duplicated (and more up-to-date) in the API docs. Also added more information about where the example data comes from, and add it for the step-by-step example.
Minor docstring fix
Update description for new definition of height
Moved catalog documentation to its own page
Tidied up docstrings for pp_catalog and ppv_catalog and added direct references in documentation