Unify macros which generate binding codes.
Clean up macros to handle html tags.
auto merge of #1074 : saneyuki/servo/macro, r=jdm
auto merge of #1075 : SimonSapin/servo/newnewcss, r=kmcallister

I believe this is all the preparatory work discussed in #1006 and #1057: The new 'style' crate implements the whole style system (including parsing, matching and cascading) and only depends on cssparser and util, so that gfx, script and main can all depend on it.

Next: porting the layout code to this. (Really, this time! I think.)
CSS: rexport types and variants for computed values.