No TTY input mode support

Both Virtual Terminal and USB ACM/CDC are implemented as TTYs, but for now, we haven't input mode control. VTs are more or less in Cooked mode, and USB is a pure RAW mode. As a consequence, a read() on USB TTY return only when the total lenght queried is read, and not after a new-line.

We should implement a relatively generic interface to handle input/output from any TTY and manage echo, line editing, special characters, etc... outside the specific TTY implementation. Some documentation about these input mode here, or on Wikipedia.