The main issue I have with this patch is that it makes the
svg import filter worse.  Some things that were supported by
the old code don't work anymore:

  - the "style" attribute leads to exceptions ("SVGHandler
    instance has no attribute 'try_add_style'").  So it's
    basically broken for SVG 1.0 files and SVG 1.1 files
    that use the style attribute which is perfectly valid in
    1.1, too.

  - The old code supported some style attributes that are
    not implemented in the patch yet (e.g. stroke-linecap,
    stroke-linejoin, font-family, font-size and text-anchor)

  - It doesn't handle the transformations correctly anymore.
    Transformation have to affect the stroke width, for
    example.

Also, I'm not sure the style handling needs to be in a
separate class in the first place.  What's the motivation
for this?

Some other things that can be improved in this patch:

 - Patches should do only one thing.  This patch contains
   not only code to handle the styling attributes, it also
   has code that appears to deal with gradient stops and
   rounded rectangles.  Those parts shoud be removed from
   this patch.  They could be submitted as separate patches,
   of course.

 - A ChangeLog entry and perhaps even some test cases that
   exercise the new features would make it easier for me to
   review and apply the patch.