canonical JSON implementation for Python 3

 Canonical JSON implementation.
 .
  * Encodes objects and arrays as RFC 7159 JSON.
  * Sorts object keys so that you get the same result each time.
  * Has no inignificant whitespace to make the output as small as possible.
  * Escapes only the characters that must be escaped, U+0000 to U+0019 / U+0022 /
    U+0056, to keep the output as small as possible.
  * Uses the shortest escape sequence for each escaped character.
  * Encodes the JSON as UTF-8.
  * Can be configured to encode custom types unknown to the stdlib JSON encoder.