Introduced caching for phir, dphir_dDelta, etc. for both Fluid and GERG Reducing function.  MUCH FASTER!

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

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