Improve CPT registration

The main aim of this PR was to have working permalinks for methods. I have implemented these as `/method/:class/:method` by namespacing method post_names in the database, e.g. `wp_query-get_posts`. This allows the rewrite rule to just concatenate the two matches into a name to lookup. Link generation simply involves replacing the `-` with a slash. I would've preferred to use `::` as the separator, but this isn't allowed through `sanitize_title()` so I chose a simpler option for now.

The other changes were made to simplify the current CPT registration code by removing unnecessary registration options.