Add some socket examples of bidirectional command helpers and pexpect

bidir_cmd_herlper.sh: Bidirectional command helper by socat.
bidir_cmd_helper.py: Bidirectional command helper by python and netcat.

pexpect-ping.py, pexpect-pong.py: Scripts for throwing Ping-Pong between
cross-connected tios.

examples/socket/bidir_cmd_helper.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+
+if [ $# -lt 2 ]; then
+    echo "Usage: $0 <socket-path> <bidirectional-command>"
+    echo "Example: $0 /tmp/tio-socket0 \"sz -b -p sample.bin\""
+    echo "Note: Please run \"tio -S <socket-path> <your-serial-device>\" beforehand."
+    exit 1
+fi
+
+SOCKET_PATH=$1
+BIDIR_CMD=$2
+
+socat EXEC:"$BIDIR_CMD" $SOCKET_PATH
+
+exit $?