Echo back characters you type based in https://mbed.org/handbook/SerialPC example
History
Echoes back to the screen anything you type; taken from :; https://mbed.org/handbook/SerialPC
2013-10-05, by felipeM [Sat, 05 Oct 2013 19:10:27 +0000] rev 0
Echoes back to the screen anything you type; taken from :; https://mbed.org/handbook/SerialPC