API update: Better site management

Our site management API has been updated with the following improvements:

• The "create a site" endpoint now accepts an optional settings object that allows site settings to be specified at creation time.
• A new "update a site" endpoint allows sites and their settings to be updated via the API.
• A new "delete a site" endpoint allows sites to be deleted via the API.
• All site endpoints now return more information about sites, and their URLs & settings.