Lightweight api

added a lightweight api (lwrtb) along with a few examples using it (both in C++ and python).
please have a look in common/bid.cc and see if the changes (requested) are acceptable and not breaking something somewhere..
LWRTB assumes objects exchanged between an agent and a router, are perfectly json-serializable. i.e:
  for an object O,  json_deserialize(json_serialize(O)) == O
which wasn't the case, hence the fixes/hacks in common/bid.cc