This was a long haul. Implemented several plugins for animation and
volumetric data to give an idea of what sort of API's work and which
do not.
* Refactored for more conventional package layout
(but importing without installing still supported)
* Put Reader and Writer classes in the namespace of the format. This
makes a format a unified whole, and gets rid of the
_get_reader_class and _get_write_class methods (at the cost of
some extra indentation).
* Refactored Reader and Writer classes to come up with a better API
for both users as plugins.
* The Request class acts as a smart bridging object. Therefore all
plugins can now read from a zipfile, http/ftp, and bytes. And they
don't have to do a thing.
* Implemented specific BMP, JPEG, PNG, GIF, ICON formats.
* Implemented animated gif plugin (based on freeimage).
* Implemented standalone DICOM plugin.