Import svg2silk from gist 5109445

See
 - https://gist.github.com/5109445
 - https://github.com/cjlano/svg
 - https://github.com/cjlano/pykicad
[svg2silk] Add README
[svg2silk] Add LICENSE: GPLv2+
[svg2silk] Add SVG and KiCad libraries as submodules