GannetMask and GannetSegment

These new functions are still a work in progress, but by way of documentation for anyone brave enough to try, here is the gist of things.

 MRS_struct  = GannetLoad({'gabafile.SDAT'},{'waterfile.SDAT'});
 MRS_struct  = GannetFit(MRS_struct);
 MRS_struct=GannetMask_Philips('gabafile.SPAR','T1.nii',MRS_struct,1);
 MRS_struct =  GannetSegment(MRS_struct);