Support for escape sequence \u

Created by: soubok

Hello, I try to decode json with binary data in a string:

  char json[] = "{\"data\":\"\\u0001\"}";
  StaticJsonBuffer<50> jsonBuffer;
  JsonObject& root = jsonBuffer.parseObject(json);
  String str(root["data"].as<String>());
  for ( int i = 0; i < str.length(); ++i )
    Serial.println((byte)str.charAt(i));

This code prints "117 48 48 48 49" (u 0 0 0 1) but I expect "1"