Add C++ object to manage library

[jowr]

Add a new C++ object that manages access to the REFPROP library. This should cover some of the code from https://github.com/CoolProp/CoolProp/blob/master/src/Backends/REFPROP/REFPROPMixtureBackend.cpp and is closely related to CoolProp/CoolProp/issues/354 and jowr/librefprop.so#21

[ianhbell]

I came up with an even better solution - load a separate copy of REFPROP into memory, in a class that is managed in C++, with all functions being exposed through the magic of variadic function argument forwarding: https://github.com/ianhbell/REFPROP-tests/blob/master/include/REFPROPtests/baseclasses.h C++11 only, but very slick.