aafig: Make Aafig directive inherit from the Image
aafig: Make Aafig directive inherit from the Image

This is a major rewrite of the extension. The Aafig directive creates an image
node with some extra information to allow a future processing to render the
aafigure image.

The Sphinx event 'doctree-read' is used to do the image rendering and update
the image URI with the proper value, based on the current builder being use.

As a side effect, now aafig directive accepts all the image directive too
(width, height, alt, align, target and class) and SVG format is properly
handled in HTML builders.
* * *
amend

sphinx-contrib/spelling,sphinx-contrib/spelling