Fetches marks
The main method for querying the marks database. You may use the following options: <ol style='list-style-type: lower-roman;'> <li>No parameters to retrieve all marks in descending chronological order (use <b>before</b> for pagination)</li> <li><b>popular</b> (and optionally <b>last_popular_id</b>) to retrieve all popular marks</li> <li><b>featured</b> to retrieve all featured marks</li> <li><b>x & y</b> to retrieve mark at specific coordinate</li> <li><b>user</b> to retrieve all marks created by the specified user</li> <li><b>collection</b> to retrieve all marks collected by the specified user</li> </ol>