Add a simple XREQ/XREP client and server for testing.
Add a zerorpc client implement.
Merge commit 'a5ec5838a67554f9f6d142de015b36d71b7b6fd1' into develop

* commit 'a5ec5838a67554f9f6d142de015b36d71b7b6fd1':
  Add a zerorpc client implement.
  Add a simple XREQ/XREP client and server for testing.