Re-organize content about XML menu tags

Created by: seancolsen

There's some good content on the hook_civicrm_xmlMenu page about the XML structure of the routing/menu system.

It would be nice to:

1. Create a new page for this content alongside framework/schema-definition/
2. Re-organize the content to be formatting more like the schema definition content
3. Edit the hook page to remove the content and link to the newly-organized content

Tim agrees.