Add message to test-this-terminal.sh

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Move tests to ‘tests/’ subdirectory

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Add an actual test-suite

Not just the naïve plausibility test.

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Actually install (termios with-exceptions)

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>