Creating and Destroying GCs

• pxl-graf-cre-create_gc: create_gc/[2,3]
• pxl-graf-cre-release_gc: release_gc/1
• pxl-graf-cre-use: Using Gcs
• pxl-graf-cre-shr: Sharing and Cloning of Gcs

The following procedures may be used to create and destroy GCs.