WIP: Simple fork exec plugin

Simple implementation for forking and getting a libchan transport.  This is the model used by @BrianBland for the new registry drivers.  The naming is likely completely wrong and this code might belong somewhere else.  It is important though to have a common location and method for libchan forking and subprocess management.  This model will likely be used in the future for running plugins as subprocess as well as a driver model

@erikh any feedback on this will be useful