Added a VirtueMart plugin

VirtueMart plugin and instructions
Merge pull request #1 from cavirtex/master

Merge latest changes (Drupal support)
Added ZenCart plugin

Added a plugin for ZenCart as well as installation instructions.
Added osCommerce support

Added support for osCommerce, and instructions for installing the
module.
Merge pull request #8 from aaronkuchma/master

Added support for VirtueMart, ZenCart, and osCommerce