Add svgToPdf.js plug-in and note about GPL Lesser 3.0

[brettz9]

Since it is a plug-in, I thought you may be open to just accepting the plug-in code as is.

[diegocr]

Brettz, you can't just throw some "plugin" code into our tree and expect it to work OOTB on jsPDF, at least i can't see there our initialization code (see the template file)

[brettz9]

It does work, but sorry, I do see it is not following your API for plug-ins. (One passes in one's own jsPDF object to svgElementToPdf().) I can rework it.

[diegocr]

I see. In fact without using our API it'd get removed from the production file as unused by our build script.

In any case, i did a bit of research and found a newer file here: https://github.com/CBiX/svgToPdf.js

So, we can just add that as a submodule, assuming that's fine to @cbix

Also, they have a PR adding it as a full-compliant jsPDF plugin (and replacement for our current sillysvgrenderer), which i guess will be merged as soon is made backward-compatible. I will also love if the jQuery dependency is removed.

Perhaps you would like to consider working with them on fixing that on their side.