Fixed REFPROP - can now compile in unicode or non-unicode on windows

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Merge branch 'master' of https://github.com/ibell/coolprop
Merge branch 'master' of https://github.com/ibell/coolprop
Fixed error messages for pressure in CoolPropStateClassSI

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>