Css support

[mikehat]

Reference the pull requests in my go-attrs branch and either my css branch in blaze-html or my blaze-css repo.

The go-attrs branch divides the go function and this one continues on that theme, adding support for the CSS style and class syntax added to blaze-html.

I also added instance Attributable Attribute so I can write code like this:

my_actions = A.onclick "click();" ! A.ondblclick "clickClick();"

H.span ! A.class_ "clickable" ! my_actions $ "try me"

Not sure if that instance could have any negative effects, but it does not affect the benchmarks.