Added coolpropsi function to EES wrapper and added COOLPROP_EES installer to CMake install listing

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

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

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Added C++ snippets to docs for API - more work needed here

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