Merge branch 'ma/pager-per-subcommand-action'

The "tag.pager" configuration variable was useless for those who
actually create tag objects, as it interfered with the use of an
editor.  A new mechanism has been introduced for commands to enable
pager depending on what operation is being carried out to fix this,
and then "git tag -l" is made to run pager by default.

* ma/pager-per-subcommand-action:
  git.c: ignore pager.* when launching builtin as dashed external
  tag: change default of `pager.tag` to "on"
  tag: respect `pager.tag` in list-mode only
  t7006: add tests for how git tag paginates
  git.c: provide setup_auto_pager()
  git.c: let builtins opt for handling `pager.foo` themselves
  builtin.h: take over documentation from api-builtin.txt

Documentation/technical/api-builtin.txt

@@ -1,73 +0,0 @@
-builtin API
-===========
-
-Adding a new built-in
----------------------
-
-There are 4 things to do to add a built-in command implementation to
-Git:
-
-. Define the implementation of the built-in command `foo` with
-  signature:
-
-	int cmd_foo(int argc, const char **argv, const char *prefix);
-
-. Add the external declaration for the function to `builtin.h`.
-
-. Add the command to the `commands[]` table defined in `git.c`.
-  The entry should look like:
-
-	{ "foo", cmd_foo, <options> },
-+
-where options is the bitwise-or of:
-
-`RUN_SETUP`::
-	If there is not a Git directory to work on, abort.  If there
-	is a work tree, chdir to the top of it if the command was
-	invoked in a subdirectory.  If there is no work tree, no
-	chdir() is done.
-
-`RUN_SETUP_GENTLY`::
-	If there is a Git directory, chdir as per RUN_SETUP, otherwise,
-	don't chdir anywhere.
-
-`USE_PAGER`::
-
-	If the standard output is connected to a tty, spawn a pager and
-	feed our output to it.
-
-`NEED_WORK_TREE`::
-
-	Make sure there is a work tree, i.e. the command cannot act
-	on bare repositories.
-	This only makes sense when `RUN_SETUP` is also set.
-
-. Add `builtin/foo.o` to `BUILTIN_OBJS` in `Makefile`.
-
-Additionally, if `foo` is a new command, there are 3 more things to do:
-
-. Add tests to `t/` directory.
-
-. Write documentation in `Documentation/git-foo.txt`.
-
-. Add an entry for `git-foo` to `command-list.txt`.
-
-. Add an entry for `/git-foo` to `.gitignore`.
-
-
-How a built-in is called
-------------------------
-
-The implementation `cmd_foo()` takes three parameters, `argc`, `argv,
-and `prefix`.  The first two are similar to what `main()` of a
-standalone command would be called with.
-
-When `RUN_SETUP` is specified in the `commands[]` table, and when you
-were started from a subdirectory of the work tree, `cmd_foo()` is called
-after chdir(2) to the top of the work tree, and `prefix` gets the path
-to the subdirectory the command started from.  This allows you to
-convert a user-supplied pathname (typically relative to that directory)
-to a pathname relative to the top of the work tree.
-
-The return value from `cmd_foo()` becomes the exit status of the
-command.