* Add get_net parameter allowing to call the function without forced flush to disk (see the discussion in #869)

* A blindfolded attempt to fix compile error on the CI server

warning messages from boost and python system header files.

get_face_chip_details() when used with the 68 point landmark model about a
month ago.  This change reverts it back to the previous behavior.  The change
was very minor, so it shouldn't matter either way.  But being consistent is
important and I'm changing it back.

mmod_rects in addition to rectangles and full_object_detections.

images that only have ignore boxes when you load into mmod_rects like it should
have been.

* remove unused variable

* modify variable type from int to size_t

* fix previous delete, we need to call chinese_whispers here but we don't need its result now

* cont layer: allow to set the number of filters at runtime
(implementation essentially copied from con layer)

* Document the new constructor cont_(num_con_outputs o), and the function set_num_filters