Unified draft of SVG-in-OT

I'm pleased to send this latest draft of SVG-in-OT out for review.

It represents a merging of the Mozilla draft specification and the one from Adobe, and it adds the long-awaited "color-by-numbers" or color palettes facility.

Note the following areas that still need more attention:

- Color spaces: is sRGB enough? Recent discussions on the OT list suggest that it may be enough, at least for now.
- Method by which color palette parameters are passed to the SVG renderer. This may change from CSS Custom Properties to a dedicated color value such as palette().
- Clarify SVG specification versions.

The attached draft is is Word since that's what OFF requires the proposals to be in; apologies in advance for any inconvenience. (Review is on; to turn it off select "Final" in the popup in the Review tab in Word.)

Best,
Sairus