Duplicate the logic of %(describe) and friends from pretty to
ref-filter. In the future, this change helps in unifying both the
formats as ref-filter will be able to do everything that pretty is doing
and we can have a single interface.
The new atom "describe" and its friends are equivalent to the existing
pretty formats with the same name.
Helped-by: Junio C Hamano <gitster@pobox.com> Mentored-by: Christian Couder <christian.couder@gmail.com> Mentored-by: Hariom Verma <hariom18599@gmail.com> Signed-off-by: Kousik Sanagavarapu <five231003@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>