added methods to remove treatment head from geomtry, and setup a CAD based phantom
added methods that the user must override in a derived class
added arguments to set a square feild off-axis
Linac now inheriting from object
Removed Mother and Daughter objects, now any Volume can be a mother, daughter or both. All top level mother objects now have to be associated with Solid which maps to a GEANT4 primitive solid.
ignoring output .phsp files
added high verbosity indicating method entry
using recursion to initialise nested geometry, disabled update geometry methods
removed unused methods
updated input file to match new scheme for building the geometry