MINOR: tevt/dev: Add term_events tool

MINOR: tevt/dev: Add term_events tool

This development tool can be used to convert a string representing a
termination event logs to its human redable representation. Several string
may be converting at a time. To do so, several arguments can be specified on
the commeand line or they can be provided on STDIN, using "-" argument.

Here is an exemple:

  > term_events f2x2f4x4 m2m4m1 e2e1 s2s1S1 E1 M1 F1
  ### f2x2f4x4 : fd:shutr > xprt:shutr > fd:snd_err > xprt:snd_err
  ### m2m4m1   : muxc:shutr > muxc:snd_err > muxc:shutw
  ### e2e1     : se:eos > se:shutw
  ### s2s1S1   : strm:eos > strm:shutw > STRM:shutw
  ### E1       : SE:shutw
  ### M1       : MUXC:shutw
  ### F1       : FD:shutw

The make target "dev/term_events/term_events" must be used to compile it.