Plant_uml example to handle nested/orthogonal machines

[ronen-fr]

Modify the plant_uml example to correctly dump both nested and orthogonal state machines.

@krzysztof-jusiak: can you direct me how to extract a readable sub-machine name from the type name?

[cmorganBE]

I had a simple state machine and the plant uml dumping code worked. Then I looked at a composite state machine and after a simple test it doesn't generate properly, it ignores sub states. Now I've started using a class as my actions require calling out to class methods for a class instance passed in when the state machine was created, and again the plant uml output is broken (this time at compile time).

This is all to say that imo having proper plant-uml output could be a huge feature for sml. I appreciate that you are trying to improve it!