Closes #24

Closes #23

Updated the pybind11 interface

Finally done

So inconsistent in naming...

Closing in with the models

Dropped three more esoteric ones with good replacements

Maybe add another smarter runtime method called model that will go through the model types and return the one that is there

Very fast in C++ (less than a microsecond for 4 outputs in the Jacobian), but 10 microseconds in Python for 2. Need to find a way to make it closer to original speed. Perhaps pass in a buffer to be populated.  That should allow the copy to be avoided. It must be the Eigen arrays that are so slow.

See #21

Add conversion routines for ideal-gas Helmholtz terms from CoolProp format

Yet another forceeval

Switch TP VLE solver to Powell's dogleg method. Might be just a little bit more reliable, but hard to tell.

See https://github.com/usnistgov/teqp/issues/9