add documentation for writing config files

Replace TODO introduced in commit 9c3c22 with documentation
explaining Git config API functions for writing configuration
files.

Signed-off-by: Tanay Abhra <tanayabh@gmail.com>
Reviewed-by: Matthieu Moy <Matthieu.Moy@grenoble-inp.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
git-push: fix link in man page

Signed-off-by: Tony Finch <dot@dotat.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'ta/doc-config'

* ta/doc-config:
  add documentation for writing config files
Merge branch 'tf/maint-doc-push'

* tf/maint-doc-push:
  git-push: fix link in man page
Git 2.1.0-rc1

Signed-off-by: Junio C Hamano <gitster@pobox.com>
RelNotes: no more check_ref_format micro-optimization

Signed-off-by: Junio C Hamano <gitster@pobox.com>
various contrib: Fix links in man pages

Inspired by 2147fa7e (2014-07-31 git-push: fix link in man page),
I grepped through the whole tree searching for 'gitlink:' occurrences.

Signed-off-by: Stefan Beller <stefanbeller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Release notes: grammatical fixes

Signed-off-by: Marc Branchaud <marcnarc@xiplink.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'mb/relnotes-2.1'

* mb/relnotes-2.1:
  Release notes: grammatical fixes
  RelNotes: no more check_ref_format micro-optimization
config: teach "git -c" to recognize an empty string

In a config file, you can do:

  [foo]
  bar

to turn the "foo.bar" boolean flag on, and you can do:

  [foo]
  bar=

to set "foo.bar" to the empty string. However, git's "-c"
parameter treats both:

  git -c foo.bar

and

  git -c foo.bar=

as the boolean flag, and there is no way to set a variable
to the empty string. This patch enables the latter form to
do that.