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

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

To avoid circular dependency in what is to come

More testing is still needed to identify other issues

I am confused...

And add test

Stopped iteration if dx values are all < 0

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