Fix backspace key and not arrow keys

[sdebionne]

Fixes #51

Also fixes the "not arrow keys" inputs (try F1-9 keys for instance) where the state machine currently get stuck in state Step::_3.

Tested with the Windows telnet client.

[daniele77]

Thank you very much for your contribution @sdebionne , I hope to find the time to check it as soon as possible.

BTW: have you tested it with linux clients, too?

[sdebionne]

I have just tested complete on Linux, with both Linux and Windows telnet client. Works fine!

[daniele77]

Just merged your PR. Thank you for your contribution, @sdebionne