Escape U+2028 and U+2029 when writing JSON as a JavaScript string literal.

U+2028 LINE SEPARATOR and U+2029 PARAGRAPH SEPARATOR are also not allowed in a JavaScript string literal. Trying to send a message with either would cause an "unexpected EOF" exception on the JavaScript side.
Merge pull request #77 from nolanw/fix-json-as-string-literal

Escape U+2028 and U+2029 when writing JSON as a JavaScript string literal