Extensions to Clojure(Script)'s unit testing framework.

EXTENSIONS TO `clojure.test/is`

There are special assertions for testing Clojure(Script) exceptions that have
been created via "ex-info".  The "(is (ex-thrown? ...))" form tests if an
exception of type ExceptionInfo is thrown, abstracting away the specific type
differences between Clojure and ClojureScript:

(is (ex-thrown? (throw (ex-info "test" {}))))

"(is (ex-thrown-with-data? f ...))" does the same thing, and also tests the
data in the exception (as returned by "ex-data") by applying it to the
function "f":

(ex-thrown-with-data?
  #(clojure.core.match/match % {:text "text"} true :else false)
  (throw (ex-info nil {:text "text"})))