Merge branch 'ks/ref-filter-describe'

"git branch --list --format=<format>" and friends are taught
a new "%(describe)" placeholder.

* ks/ref-filter-describe:
  ref-filter: add new "describe" atom
  ref-filter: add multiple-option parsing functions

diff --cc Documentation/git-for-each-ref.txt
Simple merge

diff --cc ref-filter.c
Simple merge

diff --cc t/t6300-for-each-ref.sh
Simple merge