Initial implementation of basic EtherNet/IP server/client
o Recast cpppo.server.echo tests in terms of server.network.bench
o Implement cpppo.server.enip.enip_server as a standardized
  cpppo.server.network.server_main target.  It pocesses EtherNet/IP
  frames 'til EOF, invoking the provided enip_process function on each
  valid frame, encoding and returning the results to the client.
o Default all parsed EtherNet/IP frames to have dasta context 'enip'
o Implement a simple enip_server enip_process_canned function, that
  recognizes one of the enip_test requests, and returns the canned
  response, and implement test_enip_bench in terms of it.
o Support the passage of kwargs through cpppo.server.networ.server_main,
  to allow arbitrary data to be supplied to each server thread spawned
  to support each incoming client request.