Rendering of last-returning objects wasn't implemented using a custom display
hook, like in IPyKernel, because it is not thread-safe. Instead user's code is
modified to call an external method, Base_renderAsHtml, with the object as
argument to render it. This external method can be called manually as the user
wishes.

To render a object of a given class a processor needs to be created and
associated with that class. When the class has no processor, the default one is
used to render the object's string representation. Many processors were created
for some special classes: Image class from the Image Module, Figure class from
matplotlib and all the IPython's display objects classes (Audio, IFrame,
YouTubeVideo, VimeoVideo, ScribdDocument, FileLink, and FileLinks).

The user can manually add processors as he likes using the `_processor_list`
object that is automatically injected into the code context.