Updated PromoteThis! for use with Movable Type 5.2.x and Later

Rewrote the PromoteThis for use in Movable Type 5.2.3 and later.  This
was done to facilitate upgrades of older Movable Type-based sites, and
in order to avoid continued use of Movable Type 4.  Movable Type 4.38
is going End-Of-Life at the end of 2013.

The license was changed from Artistic License (Perl) to MIT License by
After6 Services as the copyright holder and developer of the Movable
Type 5 version of this plugin.