Add echo capability

This adds the --echo parameter, which starts up an infinite loop,
printing the output of the MCU to stdout. This is useful when not
wanting to run a separate terminal to observe the MCU output.

luatool/luatool.py

@@ -178,6 +178,7 @@ def decidetransport(cliargs):
     parser.add_argument('-l', '--list',    action='store_true',    help='List files on device')
     parser.add_argument('-w', '--wipe',    action='store_true',    help='Delete all lua/lc files on device.')
     parser.add_argument('-i', '--id',      action='store_true',    help='Query the modules chip id.')
+    parser.add_argument('-e', '--echo',    action='store_true',    help='Echo output of MCU until script is terminated.')
     parser.add_argument('--delete',        default=None,           help='Delete a lua/lc file from device.')
     parser.add_argument('--ip',            default=None,           help='Connect to a telnet server on the device (--ip IP[:port])')
     args = parser.parse_args()
@@ -304,6 +305,12 @@ def decidetransport(cliargs):
     if args.dofile:   # never exec if restart=1
         transport.writeln("dofile(\"" + args.dest + "\")\r", 0)
 
+    if args.echo:
+        if args.verbose:
+            sys.stderr.write("\r\nEchoing MCU output, press Ctrl-C to exit")
+        while True:
+            sys.stdout.write(transport.read(1))
+
     # close serial port
     transport.close()