Add inline SVG (and other inline data-encoded formats?) support.

[mralexgray]

Hmm, not sure how this would work... but I'd assume sort of the same way.. The benefit, obviously would be no external linkage.. Maybe this could also be done for base64 encoded images, etc. Basically the ability to just Inline the image data.

Here's a random SVG to aid in testing if the issue is accepted.