Documented async functions

Author: kmvanbrunt

docs/unfreefeatures.rst

@@ -189,3 +189,26 @@ Exit code to shell
 The ``self.exit_code`` attribute of your ``cmd2`` application controls
 what exit code is sent to the shell when your application exits from
 ``cmdloop()``.
+
+
+Asynchronous printing
+=====================
+``cmd2`` provides two functions to provide asynchronous feedback to the user without interfering with
+the command line. This means the feedback is provided to the user when they are still entering text at
+the prompt. To use this functionality, the application must be running in any terminal that supports
+VT100 control characters and readline. Linux, Mac, and Windows 10 and greater all support these.
+
+_async_alert()
+    Used to display an important message to the user while they are at the prompt in between commands.
+    To the user it appears as if an alert message is printed above the prompt and their current input
+    text and cursor location is left alone.
+
+_async_update_prompt()
+    Updates the prompt while the user is still typing at it. This is good for alerting the user to system
+    changes dynamically in between commands. For instance you could alter the color of the prompt to indicate
+    a system status or increase a counter to report an event.
+
+
+The easiest way to understand these function is to see the AsyncPrinting_ example for a demonstration.
+
+.. _AsyncPrinting: https://github.com/python-cmd2/cmd2/blob/master/examples/async_printing.py