Changes

• changed function name from process_grid to grid3d

• changed function signature from:

  def process_grid(tot_set, i_stack, q_min=None, q_max=None, dqn=None):
  

  to

  def grid3d(q, img_stack,
             nx=None, ny=None, nz=None,
             xmin=None, xmax=None, ymin=None,
             ymax=None, zmin=None, zmax=None):