Fixed one bug with pseudo-pure saturation calls

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Corrected hydrogen viscosity as per discussion with Marcia

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Tidied up some transport tests

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Merge branch 'master' of https://github.com/coolprop/coolprop