Add CSS2.1 properties to CSS index

Note: In Markdown format at this stage.
Add CSS4 Color properties
Add CSS3 Backgrounds and Borders properties
Add CSS3 Images properties

…and some re-ordering to B&B that I didn’t save previously. Whoops.
Add CSS3 Marquee
Add CSS Multi-column properties
Add CSS Speech

Need to check if any properties from CSS2.1 appendix need to be removed
(such as volume.) This spec is old, so need to check it is still
current too.
Add CSS Flexbox properties
Add CSS3 Cascade properties
Add CSS3 Fonts properties
Add CSS Animation properties
Add CSS Masking properties
Add CSS3 Text properties

Still need to add CSS4 properties (unstable, but a bunch are
implemented)
Add CSS3 Fragmentation properties
Add CSS Shapes properties
Add CSS Transforms properties
Add CSS Transitions properties
Add CSS Custom Properties and CSS3 Writing Modes properties
Add CSS Compositing properties
Add CSS3 Box Alignment properties