Kill raw input reader's child by process group.

This should help on systems where the default shell (e.g. dash on
Ubuntu) fork-execs in order to run commands.  In that case, we were
just killing the shell and the shell would exit without killing
the actual process corresponding to command that was requested.
Setting a process group for the shell exec'd from Bro and killing
by process group should help clean everything up since process group
will be inherited by any procs that shell fork-execs.
Update the lines included from events.bif.bro.

Previously listed connection_established and connection_finished which
are no longer in place in events.bif.bro.
Spelling corrections.

Apparently I am unable to spell "separate".
Rewrite the MHR detection description.

Now that the MHR script uses the file analysis framework, the
description needed to be rewritten to reflect the changes.  Robin
commented that he didn't feel the MHR script was a good introductory
script and he might be right, however, I couldn't find one that was
easier to explain.
Include a better description for detect-MHR.bro

I added a better more concise and accurate description of what is going
on behind the scenes of detect-MHR.bro to not only bring it into line
with the Files framework but to help make it a bit more clear as to
where the various responsibilities lie.
Spelling corrections.
Merge remote-tracking branch 'origin/topic/jsiwek/raw-exec-pgrp'

* origin/topic/jsiwek/raw-exec-pgrp:
  Kill raw input reader's child by process group.

BIT-1081 #merged
Merge remote-tracking branch 'origin/topic/srunnels/documentation'

* origin/topic/srunnels/documentation:
  Spelling corrections.
  Include a better description for detect-MHR.bro
  Rewrite the MHR detection description.
  Spelling corrections.
  Update the lines included from events.bif.bro.
Updating baselines for doc changes.
Updating submodule(s).

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Updating submodule(s).

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Updating submodule(s).

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Updating submodule(s).

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