Very subtle problem with handling derivatives at zero density

Another bugfix release is needed

This reverts commit a8689209.

Try to push this hotfix today

[] is no longer a valid kmat

Closes #34

Closes #38

Closes #40

Helpful for debugging

Tests should pass again

Add Saft-VR-Mie EOS

Can do binary mixture tracing now!

Seems to be working

To allow for providing the mole fractions, in order to allow for the use with mixtures.

Doesn't have the claimed critical temperature; closer before fixing the erroneous coefficient

Still can't trace isotherms with mixtures yet