Created a REFPROPSI function that takes and returns SI units

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Removed acetic acid REFPROP alias

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

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Cleanup of insanity of Props overloads for kSI and SI units

Removed Props() overload with all char strings; Removed Props(char*,char*) and Props(std::string, std::string) overloads.  IProps and Props now call IPropsSI and PropsSI.

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