WIP: CPS proof of concept

Add a command to load a CPS file from an explicit path.

This is intended as a proof of concept ONLY and will likely never appear
in an official release (although much of the code will probably be
adapted). Because virtually no projects currently ship CPS (and this has
not been tested with the one project known to the author that actually
does ship CPS), it is expected that demonstration CPS files may be
provided independent of other artifacts. Therefore, the demonstration
command also takes the package prefix as an argument.