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

It avoids a quiet copies throughout the interface

Add routine for TP flash for binary mixture, to solve for molar concentrations (and therefore mole fractions)

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

More testing is still needed to identify other issues

Problem: compile-time time arguments remapped to runtime arguments, in future the runtime arguments should come after the model

* Add methods for calculation of pure fluid critical points

* Pass the template arguments along

* Expose the values and Jacobian

* Add partial molar volume as a possible output

* And expose to python

Based largely upon: https://pubs.acs.org/doi/abs/10.1021/acs.iecr.1c04703

Switch critical tracing to use one of the molar concentrations as the fixed parameter when polishing

Expose more critical methods in pybind11 interface

Break up pybind11 interface into separate compilation units (not as beneficial as hoped); still very slow