Use hiccup for templating

[paintparty]

The current hiccupish syntax tends to get a little noisey for multi-line messages with variously styled elements.

Replace the current convention with hiccup:

(bling
  [[:br]
   [:p "Value for the "
    [:bold (str ":-" opt-sym)]
    " option must pass this predicate:" [:br]
    [:bold (if (set? pred) (str pred) pred)]]
   [:br]
   [:p "Check out the docs for more info:" [:br]
    [:a {:href "my-url"} "my-url"]]]