update console-printed description of prism to include center and report axis in cartesian (not prism) coordinate system (#22)

Author: Homer Reid

utils/geom.c

@@ -2482,10 +2482,11 @@ void display_prism_info(int indentby, prism *prsm)
   int num_vertices  = prsm->vertices.num_items;
   double height     = prsm->height;
   vector3 z0        = {0.0, 0.0, 1.0};
-  vector3 axis      = matrix3x3_vector3_mult(prsm->m_c2p,z0);
+  vector3 axis      = prism_vector_p2c(prsm,z0);
+  vector3 center    = prism_coordinate_p2c(prsm,vector3_scale(0.5*height,z0));
 
-  printf("%*s     height %g, axis (%g,%g,%g), %i vertices:\n", indentby, "",
-          height, axis.x, axis.y, axis.z, num_vertices);
+  printf("%*s     height %g, axis (%g,%g,%g), center (%g,%g,%g), %i vertices:\n", 
+          indentby, "", height,axis.x,axis.y,axis.z,center.x,center.y,center.z,num_vertices);
   matrix3x3 m_p2c = matrix3x3_inverse(prsm->m_c2p);
   int nv;
   for(nv=0; nv<num_vertices; nv++)