Fix division symbol.

- In ns-snap munge the cljs.core// symbol before and after read-string
  to avoid the Clojure-side exception.
- For cljs.core/name and cljs.core/namespace, correctly handle / and
  cljs.core//. This brings these functions in sync with
  clojure/src/jvm/clojure/lang/Symbol.java
Misc README updates.