Introduce optional prefixes "width=" and "position=" for the align atom
so that the atom can be used as "%(align:width=<width>,position=<position>)".
Add Documentation and tests for the same.
Helped-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Karthik Nayak <Karthik.188@gmail.com> Reviewed-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>