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

Should speed up compilation a smidge

* Add methods for calculation of pure fluid critical points

* Pass the template arguments along

* Expose the values and Jacobian

Couple of inlines are needed to avoid duplication of functions between compilation units

Test that all derivatives match with those of finite differentiation to numerical precision (they do!)

needed a force eval, () needed to be moved

Method from Ulrich Deiters, superancillary from our new paper

See #2

See #2

See #2

And Python wrapper and tests

Add test for neff; it is undefined for vdW EOS, interesting

Isochoric derivatives moved into their own namespace