More FreeBSD Ports goodness

This pull req does the following:

1. Adds an argument to ``salt.modules.freebsdports.showconfig()`` which allows you to see the default build options for a given port.
2. Adds new ``search`` and ``list_all`` functions to the ``freebsdports`` execution module.
3. Adds a new ``ports`` state module, with a single ``installed`` state. (a ``deinstalled`` state will come later)
4. Fixes a sphinx build warning in the ``win_repo`` execution module.