add description of samples field to manual page

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
add yaml output format support

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
add simple regression test suite

Not much, but at least should catch stupid formatting errors.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>