fully integrated `libuv` networking features, more examples

• added methods/functions:
  net_operation, dns_address, dns_name, dns_record, listener_task
net_listen, net_client, net_server, net_stop, net_accept, net_connect, net_bind
net_read, net_write, net_close, net_peer, net_request, net_response
  These functions to methods behavior depends on uri scheme, and either a libuv object or stream/fd/socket resource passed in.
• added more upstream libuv network tests and examples.
• added stateless_task function to cause tasks/coroutines not to keep task completion state or data.
• added NetworkAssistant class for handling network message processing, works similar to PSR-7
• code clean up, corrections
• added an PHP version of Python and NodeJS sync/async examples from https://medium.com/@interfacer/intro-to-async-concurrency-in-python-and-node-js-69315b1e3e36
• Refactoring for examples not working as expected
• insure progressTask only execute if actual data is returned
• added two utility functions similar to NodeJS, Python usage as random_uniform and timer_for
• update readme to show php version same as nodejs and python