It works!

* Add methods for calculation of pure fluid critical points

* Pass the template arguments along

* Expose the values and Jacobian

Covers all the cases, one at a time

To check whether you have gotten to the critical point

For isothermal VLE tracing

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

Fix the parametric tracer; it was switching directions because the dot product check was not implemented properly.

TODO: add some tests to ensure this stays fixed, maybe P-R for CO2+ethane?

TODO: apply polishing in another variable if constant composition polishing fails