Escape JSON string correctly according to [rfc4627]

Fixes #113

This code escapes quotation mark, reverse solidus, and the control
characters (U+0000 through U+001F) in the json string according to
[rfc4627](http://www.ietf.org/rfc/rfc4627.txt) in addition, this code
will escapes LINE SEPARATOR (U+2028) and PARAGRAPH SEPARATOR (U+2029).
Formatted escape_json_output() routine.