Add line response feature

Add a simple line response feature to make it possible to send e.g. a
command string to your serial device and easily receive and parse a line
response.

This is a convenience feature for simple request/response interaction
based on lines. For more advanced interaction the socket feature should
be used instead.

The line response feature is detailed via the following options:

 -r, --response-wait

Wait for line response then quit. A line is considered any string ending
with either CR or NL character. If no line is received tio will quit
after response timeout.

Any tio text is automatically muted when piping a string to tio while in
response mode to make it easy to parse the response.

 --response-timeout <ms>

Set timeout [ms] of line response (default: 100).

Example:

Sending a string (SCPI command) to a test instrument (Korad PSU) and
print line response:

 $ echo "*IDN?" | tio /dev/ttyACM0 --response-wait
 KORAD KD3305P V4.2 SN:32477045

README.md

@@ -46,6 +46,7 @@ when used in combination with [tmux](https://tmux.github.io).
  * Activate sub-configurations by name or pattern
  * Redirect I/O to file or IPv4/v6 network socket for scripting or TTY sharing
  * Pipe input and/or output
+ * Support for simple line request/response handling
  * Bash completion
  * Color support
  * Remapping of prefix key
@@ -87,6 +88,8 @@ The command-line interface is straightforward as reflected in the output from
     -c, --color 0..255|bold|none|list      Colorize tio text (default: bold)
     -S, --socket <socket>                  Redirect I/O to file or network socket
     -x, --hexadecimal                      Enable hexadecimal mode
+    -r, --response-wait                    Wait for line response then quit
+        --response-timeout <ms>            Response timeout (default: 100)
     -v, --version                          Display version
     -h, --help                             Display help