Generalization of state.run to handle DFA
o Prevent re-entrancy of dfa, since it contains operational state
o Support copying of a state in constructor
o Make state.terminal a property to support dfa (depends on sub-machine)
o Support transitions based on symbol encoding which results in multiple
  underlying symbols
o The state.run now supports delegate, to allow implementation of
  derived classes (eg. dfa) that produce a stream of transitions.
o Bracket entry/exit of state in initialize/terminate methods
o When producing a state machine from a regular expression, create a
  proxy initial state which consumes no input and has the same outgoing
  transitions as the greenery.fsm initial state, to validate the initial
  regular expression symbol.
o Make dfa_base a mixin, to allow dfa_... classes based on any availalbe
  state class specialization.
o Name greenery.fsm based regular expression machinery class cpppo.regex
  instead of cpppo.fsm, to clarify its function.
o Create cpppo.server.network generic server_thread, server_main and
  bench functions to impelement standardised servers based on
  cpppo.automata state machinery, and implement echo and tnet tests
  using them.