[GSoC][RFC PATCH 0/6] Add --subject-extra-prefix flag to format-patch

Hi!

This is a "scratch-my-own-itch" patch, adding a new flag to format-patch. This flag allows the user add an extra prefix to the subject, placed before the actual prefix, like the "[GSoC]" in the subject of this patchset.

This is specially targeted for new users or developers from mentoring projects like GSoC or Outreachy. Currently, if we want to add to the subject something like "[Newbie]", "[GSoC]" or "[Outreachy]", we need to perform some hacks like passing --subject-prefix="GSoC][PATCH" or changing it manually in the patch content.

With this new flag, this patchset could be created by using:

`git format-patch -6 --subject-extra-prefix="GSoC" --rfc --to="..."`

This would be only a feature request but I thought it would be better to present a first solution, so I'm sending my implementation as a RFC patchset.

Thanks!

Lucas Seiki Oshiro (6):
  builtin/log: add subject-extra-prefix flag to format-patch
  builtin/log: die if -k and --suject-extra-prefix are used together
  revision: add subject_extra_field to struct rev_info
  builtin/log: fill subject extra prefix in format-patch
  log-tree: add subject prefix in output email subject
  t4014: add tests for the new flag --subject-extra-prefix

 builtin/log.c           |  7 +++++++
 log-tree.c              | 12 ++++++++----
 revision.h              |  2 ++
 t/t4014-format-patch.sh | 40 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 57 insertions(+), 4 deletions(-)