[matplotlib-devel] Small fix for SVG backend

[Dieter W. <di...@ue...>]

Hi,
I tried to use matplotlib.rcParams['svg.embed_char_paths'] = False in
order to have editable text in exported SVG, but there was an encoding
issue and the file data could not be written (traceback appended).

Therefore I exchanged the XML character escaping from sax in
backend_svg.py with python's native XML escape capability (see appended
diff), and voilà it works!

The conversion of mathtext to SVG is still not so nice because specific
fonts (cmmi10, cmr10, cmsy10) are used that encode mathematic symbols
with other unrelated characters. The formula display will totally break
if these fonts aren't installed, and editing is a pain. It would
therefore be great if unicode characters were used so that the correct
display is not so much dependent on those specific fonts. Would this
introduce other problems and where would be the best point to make that
change?

Greetings,
Dieter