Add feature for CSS Typed OM

[queengooborg]

This PR adds a feature for the CSS Typed OM Level 1.

[jamesnw]

I'd propose a different approach- many of these keys should be part of separate features. For instance, api.CSS.cap_static should be part of the cap feature, similar to how the highlight feature contains api.CSS.highlights_static.

This feature should contain the keys that are related to CSS syntax and wouldn't be part of other features. Some examples-

• api.CSSNumericArray
• api.CSSNumericValue
• api.CSSUnitValue.value

Some of the keys here can be added to existing features, but there are others like rcap that will still need to be created.