Include some functions to get messages from a interface

[guyikcgg]

task-based VS interrupt-based

This functions should get data from a shared interface (such as UART or TCP/IP connection), giving back the whole text for the command + arguments in a buffer.
If some pre-defined particular data is received (such as Ctrl+C), these functions should interact with commands, requesting them to stop.

Then, there will be other functions to recognize the commands and launch the corresponding functions.
Commands should react to signals from the shell (such as Ctrl+C).