svg rendering

[Keiron Liddle <ke...@aftexsw.com>]

After wrestling with the ever increasing PDFRenderer I have decided to
put all the SVG rendering for PDF in a separate class.
This will at least make it much easier to manage and should also keep
the svg code out of the way of the other pdf rendering.
I can also easily deal with things like patterns where isolating the
rendering to a string (buffer) is much easier.

I anticipate that the same sort of thing will be done for the AWT
rendering, which also means that the rendering can be done to a graphic
for applying effects on.

Radial Gradient rendering is improved and works for simple examples. I'm
not sure how to handle elliptical gradients (when the shape is dependant
on the shapes bounding box)

Pattern shading is not too far away, much simpler than I thought (thanks
to the already functioning PDF data structures).

Keiron