Add the Schmidt-Wenzel EOS about thermo

[CalebBell]

Hi Alex,
Adding an equation of state is pretty involved and counts on a whole lot of things being correct about the implementation.

For higher accuracy, Helmholtz models as implemented in CoolProp are recommended; for multicomponent mixtures, the PR and family are the recommended models because they can still be relatively fast with many components. I am not sure how this EOS works with mixtures.

[alexchandel]

Schmidt-Wenzel is technically a small modification of SRK / PR, and thus its implementation will appear very similar. It's also as fast as PR, but with greater accuracy.

The SW EOS supports the same range of mixing rules & combining rules (van der Waals, Wang-Sandler, Huron-Vidal, etc) as VDW, PR, & SRK. Like alpha functions, these aren't specific to an EOS.

[CalebBell]

Hi Alex,
You have posted quite a few times and helped several users. Thank you for that. I have released a new, comprehensive redesign of the library with a new interface that should avoid some of the fundamental issues that were previously present.

It's not realistic to do all the fixes and features all the time. If you are still interested in this feature though, I can provide advice and help for you to develop it.
Sincerely,
Caleb