Suggestion: functionality in mp1 for returning a string of the phase

[jranalli]

This is potentially a wormhole, but I think it might be useful to have a function that computes the phase for multiphase substances, and/or make it an option to have the string return from the quality function. It is of course easy to determine for yourself, but requires several calls back to pyromat after you get a quality of -1.

It also occurred to me that this might be useful if you ever need to case out certain types of iteration algorithms. For example, fixing state properties given T & h is hard outside the steam dome, but trivial underneath. Whether there are cases where knowing liq vs gas vs supercritical can be useful to the numerical approaches I can't say off the top of my head, but it seems possible. One thing that does come to mind is that you'd expect finding things as a function of T&d to be stiff in the liquid region due to incompressibility, so maybe knowing that would help determine expected uncertainty/accuracy in that region?

Even if it doesn't provide anything for casing out other operations, I can say that it is definitely useful pedagogically.