This patch moves the Selector object model closer to the specification
objects in Selectors Level 4.
A "Selector" in LibHTML is now a { Vector<ComplexSelector> }, which is
a { Relation, CompoundSelector }. A CompoundSelector is really just
a Vector<SimpleSelector>, and SimpleSelector is "Component" renamed.
This makes a lot more selectors actually match on the Ubuntu Apache2
default homepage. :^)
This patch adds a[foo] and a[foo=bar] attribute selectors.
Note that an attribute selector is an optional part of a selector
component, and not a component on its own.
This is currently very aggressive. Whenever the Document's hovered node
changes, we invalidate all style and do a full relayout.
It does look cool though. So cool that I'm adding it to the default
stylesheet. :^)
