Tweaks to exponentation in the prelude, change __make-instanceof to __get-instanceof.
remove __async-result and __async-iter-result, making whether or not it requests a "result" a boolean argument.
for item from iter now works with arrays, but for item in array is far more efficient. Change the internals of WeakMap to be O(1) on all operations as long as the key is extensible, otherwise falling back to the O(n) mechanism.
If an object prevents extensions while acting as a key in a WeakMap, it will properly switch its treatment from O(1) key[secret] = value to storing on an array giving O(n) times and leaky memory.
Add multi-codepoint string unicode escapes, e.g. "\u{20bb7}", which turns into two UTF-16 code points. Reference: http://wiki.ecmascript.org/doku.php?id=harmony:unicode_supplementary_characters