The links to user profiles in parsed mentions are incorrect when the render occurs on a page in a different directory than the MyBB instance (e.g., custom pages not within the MyBB folder on the server).

For instance, a board at https://google.com/mybb has a custom page at https://google.com/mycustompage.
Expected result: The mention link renders as https://google.com/mybb/member.php?uid=1.
Actual result: The mention link renders as https://google.com/mycustompage/member.php?uid=1.

#255 fixes this issue.