Add macros and :do-attr now redundant (thanks @borkdude)

* Add `with-timeout` and `with-init!` macros.

* It is now unnecessary to use the :do-attr syntax.

  For example:
    (a :do-attr (cell= {:href url-cell}) "i'm a link")
  can now be simply,
    (a :href url-cell "i'm a link").

  This works for all `do!` multimethod dispatch methods, too.

  For example:
    (p :do-class (cell= {:active active-cell}) ...)
  can now be,
    (p :class (cell= {:active active-cell}) ...).