Minor cleanup.
Graph cleanups.
Refactor 'fiducial' into 'Fiducial' to make it clearer that it's a class.  Also isolate VaginalDisplay to its own file to eliminate circular dependencies.
Abstract paravaginal gap computation into its own function.
Add ability to normalize to inter-ischial spine width.
Refactor 'fiducial' into 'Fiducial' to make it clearer that it's a class.  Also isolate VaginalDisplay to its own file to eliminate circular dependencies.
Add the ability to plot paravaginal gap in a separate graph.