Houdini 18.0 compatibility

Hello folks !

All the tools on cgtoolbox.com are now compatible with Houdini 18.0 which was released last week !

For Python 3.7 support, it is scheduled for beginning of next year ( 2020 ). In the meantime, there is no guarantee that the scripts will work with the Python 3.7 build of Houdini 18.0.

GuillaumeJ