Arbitrary Mimetypes Handing in Terminal

When using IPython terminal it is now possible to register function to handle arbitrary mimetypes. While rendering non-text based representation was possible in many jupyter frontend; it was not possible in terminal IPython, as usually terminal are limited to displaying text. As many terminal these days provide escape sequences to display non-text; bringing this loved feature to IPython CLI made a lot of sens. This functionality will not only allow inline images; but allow opening of external program; for example mplayer to "display" sound files.

So far only the hooks necessary for this are in place, but no default mime renderers added; so inline images will only be available via extensions. We will progressively enable these features by default in the next few releases, and contribution is welcomed.

We welcome any feedback on the API. See :ref:`shell_mimerenderer` for more informations.