#21 Use rsvg-convert instead of inkscape for SVG conversion

[Matej Cepl]

(Originally from Fedora, https://src.fedoraproject.org/rpms/dblatex/raw/rawhide/f/dblatex-0.3.11-replace-inkscape-by-rsvg.patch )

rsvg-convert is much more lightweight than Inkscape, because it is just a conversion utility not a full-size SVG editor.