[css-props-vals] First iteration of L1 spec

Hey everyone,

Tab, Shane, Ian and I were able to get together on a video call today and hashed out some of the details regarding what the custom properties and values API can provide, its expected data structures, potential hurdles and some examples.

Please feel free to provide your feedback regarding the API design and any potential issues we didn't consider.

http://dev.w3.org/houdini/css-properties-values-api/

Thanks,
Greg