Merge pull request #315 from CoolProp/develop

Added surface tension for HFC fluids.  Closes https://github.com/CoolProp/CoolProp/issues/306
Delete .travis.yml

as per #73 travis is being removed for now, might be back later if anyone knows how to make best use of the resouce
Merge pull request #316 from CoolProp/develop

Added docs for the use of partial derivatives (first at least).  Closes ...
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...
Removed the source builder and added the zipping to the server in the release script.
Finish ReplaceSourceBuildbot