implemented most parts of zeromq interface

done:
  * DYNAMIXEL_RQ_PING
  * DYNAMIXEL_RQ_WRITE_DATA
  * DYNAMIXEL_RQ_REG_WRITE
  * DYNAMIXEL_RQ_REG_ACTION
  * DYNAMIXEL_RQ_RESET

Typechecking and error codes added.
Check for invalid lists.