CSS vars and observables

[streamich]

Create an addon which works with CSS vars and observables, maybe something what JSS does:

http://cssinjs.org/observables

[streamich]

Experimental API has been implemented here:

• https://github.com/streamich/nano-css/pull/49

See these files:

• https://github.com/streamich/nano-css/blob/master/addon/cssom.js
• https://github.com/streamich/nano-css/blob/master/addon/ref.js