Water viscosity can now be evaluated at the critical point

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Slight improvement in water critical conductivity term - all within 0.02% error now

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Updated coefficient for transport correlations, HS reference code in main.cxx

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

Conflicts:
	src/Helmholtz.cpp
	src/main.cxx

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