Can get long name from the incompressible fluid

Something like

rr = get_fluid_param_string("INCOMP::MEG","long_name");

Closes https://github.com/CoolProp/CoolProp/issues/244

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

src/Backends/Incompressible/IncompressibleBackend.h

@@ -124,6 +124,8 @@ public:
     long double calc_fraction_max(void){return fluid->getxmax();};
     long double calc_T_freeze(void){
         return fluid->Tfreeze(_p, _fractions[0]);};
+        
+    std::string calc_name(void){return fluid->getDescription();};
 };
 
 } /* namespace CoolProp */