Fixed problems with HAPropsSI when wetbulb is an input by converting call to Brent.  Slow but steady.

Closes https://github.com/CoolProp/CoolProp/issues/311

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Merge pull request #317 from CoolProp/hapropssi_error_wetbulb

Fixed problems with HAPropsSI when wetbulb is an input by converting cal...