A resubmission of commit 8e4f748 in PR #2403 and PR #2444 and continues
the work in #2690 implementing Python bindings to the flow simulator.
The Python step() method advances the simulator one report step. Before
calling step() for the first time, step_init() must have been called.
A resubmission of commit 11eaa3d7 in PR #2403 and PR #2443 and continues
the work in #2555 implementing Python bindings to the flow simulator.
The step_init() method initializes the simulation. It is required for the
Python script to run step_init() before calling the step() method (which
will be implemented in a later commit).
