The Class "Evaluator"
=====================

The class "Evaluator" runs an evaluator in a child process. 

When it is opened, Evaluator has four states:

property:       STARTED  PROCESS_EXISTS  PROCESS_PAUSED
  - Ready:        0                                       no best move known
  - Running:      1         1             0               process running
  - Paused:       1         1             1               process exists but stopped
  - Finished:     1         0                             process terminated and best move known

The state can be determined by checking the property above.  

Internally these properties correspond to:

   STARTED=   started
   PROCESS_EXISTS=  IO_Child_Process::Is()
   PROCESS_PAUSED=  IO_Child_Process::Paused()



 State Diagram:
    /-----------\                /---------------\
    |  Ready    |<-\-reset-------|   Finished    |
    \-----------/  |             \---------------/
     /|\ |         |                    /|\
      | start      |                     |
      |  |       reset                   |
      |  |         |                     |
      |  |      /-------------\          |
      |  \----->|  Running    |--stop----/
      |         \-------------/          |
      |           |      /|\             |
      |         pause     |              |
      |           |    continue          |
    reset         V       |              |
      |         /-------------\          |
      \---------|  Paused     |--stop----/
                \-------------/

The combination of RESET + START is called RE_START.
