Rewrite of documentation for recip.process_to_q

- Exposed the frame_mode variable as an input parameter to
  recip.process_to_q
- Added new tests to make sure that bad entries for frame_mode
  actually fail and that good entries do not raise an exception
The dimension used before is like

detector_size : tuple
2 element tuple defining the number of pixels in the detector. Order is
+        (num_columns, num_rows).

a litte inconsistent here.