Use opkg module as basis for macports module

This module is pretty simplistic, it is derived from the opkg module. It is
also named dports (as the command is 'port'). The reason for prefixing the
module with 'd' is so that it is not confused with the *BSD port systems and
the commands that they might have.

Installation of packages work, uninstallation is hit or miss as macports doesn't uninstall dependant packages; this is to prevent users from shooting themselves when uninstalling things.

Things to follow after this commit might include

* renaming the module if needed
* add activate/deactivate states
* add a "uninstall inactive" command/alias/state to purge all present and deactivated packages

perhaps a re-factoring of the other modules and this one as this module is derived from a derived module?