Enhanced example for memory usage executor, sync for all docs

It seems, html help already had one free instance with -s option for persistance,
though still used inner non-persistant chain for humanized output.

doc/tint2.1

@@ -831,10 +831,11 @@ execp_markup = 1
 .PP
 .RS
 .nf
+# "stdbuf -oL" noticed to give better performance than fflush() from awk code
 execp = new
-execp_command = free | awk '/^\-/ { printf "Mem: '$(free \-h | awk '/^Mem:/ { print $2 }')' %.0f%%\\n", 100*$3/($3+$4); fflush(stdout) }'
-execp_interval = 5
-execp_continuous = 0
+execp_command = free -b -s1 | stdbuf -oL awk '/^Mem:/ { printf "Mem: %.1fGi %.0f%%\n", $2 / (2^30), 100 * ($2 - $7) / $2 }'
+execp_interval = 1
+execp_continuous = 1
 .fi
 .RE
 .SS Network load