Makefile: Add test-verbose and test-suite-verbose targets

All the TAP output, every time the suite runs might be too much. This
way, you can have it both. The default is to be quiet.

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
README: More about testing

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Add new test-file: struct-termios.t

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

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
gen-gps: Remove superfluous newline

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Cosmetics: Add a ‘tap/comment’ call

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
plausibility tests: Don't run if stdin isn't a terminal

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