Fix pkill man page (#427)

* Cleans up an ambiguous example in the man page

Using parameter -f to 'pkill' kills the first program which contains the mentioned
'rec' string in its command line. That may not be the program with the
name 'rec'.

* Replace backticks with $() in scripts/soundlog

As backticks are generally hard to see, use the synonymous $() construct
to generate the name for the audio file.  $() is preferred for capturing
the output of a command into a shell variable.

---------

Co-authored-by: Nate Bargmann <n0nb@n0nb.us>

scripts/play_vk

@@ -27,7 +27,7 @@ trap 'kill -s KILL $PID' TERM INT
 # mute mic
 #amixer -c 0 set Mic mute -q
 
-# play file on the default sound device in background, so signals can be catch
+# play file on the default sound device in background, so signals can be caught
 # by the 'trap' instruction above
 
 # SoX play utility syntax

scripts/soundlog

@@ -8,7 +8,7 @@ trap 'kill -s INT $PID' TERM USR1
 while [ -f $HOME/.VRlock ]
 do
 		# store recorded files in actual directory
-		filename=`eval date +%d%H%M`".au"
+		filename=$(eval date +%d%H%M)".au"
 		if test -f $filename
 		then
 			sleep 10

tlf.1.in

@@ -606,7 +606,7 @@ shown):
 .
 .P
 .EX
-/usr/bin/pkill \-f rec
+/usr/bin/pkill \-x rec
 .EE
 .
 .P