Added Line.Builder.length.
Defer validation to next UI tick.

Otherwise we invalidate and revalidate the same line half a dozen times as
grammar code mode re-applies styles to a given line of code.
Added Chars.Category and Buffer.regionAt.
Added Line.Builder.appendWiths.
Added Resource.names.
Added Tags.isEmpty.
Better Line.toString.
Compactify.
Allow fns to defer to other fns.

If a fn doesn't handle a trigger, it can return false to indicate as much and
any other fns bound to the same trigger will be tried.
Wrapped long line.