Support for instantiating actions and parsing plans

[haz]

Is your feature request related to a problem? Please describe.
We'd like to be able to parse plans using the standard IPC format, and also (as a pre-requisite) instantiate a lifted action with a dictionary mapping the parameters to constants/objects.

Describe the solution you'd like
New functionality to .instantiate a lifted action, and new plan parser.

Describe alternatives you've considered
Considered other libraries, but this limited functionality should be offered natively with pddl.