Added EPL license notices for clj-v8

Following discussion in #12, I've made this change with authorization from @pbiggar (given there was no pre-existing license). It adds:

* A copyright notice for "the clj-v8 authors", similar to how v8 does it.
* An authors list including @magnars and me (assuming this PR gets merged).
* EPL 1.0 for all parts of clj-v8 (same as Clojure), except for v8 itself.
* Retrospective application of EPL 1.0 for clj-v8.
* A quoted reproduction of v8's terms, just in case.

Does this look reasonable? (Disclaimer: I am not a lawyer, etc.)