removed traits
refactor: a bunch of renaming to remove noisy words

Any word that didn't add extra meaning was removed to decrease the
verbosity and confusion.

types:

  incoming_state -> read_state
  outgoing_state -> write_state

free functions:

  incoming_request_continue_required -> request_continue_required
  incoming_request_upgrade_desired -> request_upgrade_desired

embedded_server_socket:

  incoming_state -> read_state
  outgoing_state -> write_state
  outgoing_response_native_stream -> write_response_native_stream
  async_incoming_request_read_message -> async_read_request
  async_read_some_body -> async_read_some
  async_outgoing_response_write_message -> async_write_response
  async_outgoing_response_write_continue -> async_write_response_continue
  async_outgoing_response_write_metadata -> async_write_response_metadata
removed fisttest
removed embedded_server_socket_acceptor

This wrapper don't add any value and is too restricted. In fact, it
cannot be used to work with SSL connections.
refactor: embedded_server_socket -> basic_socket

The embedded_server prefix no longer fully captures the abstraction's
purpose given the fact that the abstraction can be extended to also
support an HTTP client.

A socket typedef for tcp was also created.