Add git-upload-archive

This command implements the git archive protocol on the server
side. This command is not intended to be used by the end user.
Underlying git-archive command line options are sent over the
protocol from "git-archive --remote=...", just like upload-tar
currently does with "git-tar-tree=...".

As for "git-archive" command implementation, this new command
does not execute any existing "git-{tar,zip}-tree" but rely
on the archive API defined by "git-archive" patch. Hence we
get 2 good points:

 - "git-archive" and "git-upload-archive" share all option
   parsing code.

 - All kind of git-upload-{tar,zip} can be deprecated.

Signed-off-by: Franck Bui-Huu <vagabon.xyz@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-upload-archive.txt

@@ -0,0 +1,37 @@
+git-upload-archive(1)
+====================
+
+NAME
+----
+git-upload-archive - Send archive
+
+
+SYNOPSIS
+--------
+'git-upload-archive' <directory>
+
+DESCRIPTION
+-----------
+Invoked by 'git-archive --remote' and sends a generated archive to the
+other end over the git protocol.
+
+This command is usually not invoked directly by the end user.  The UI
+for the protocol is on the 'git-archive' side, and the program pair
+is meant to be used to get an archive from a remote repository.
+
+OPTIONS
+-------
+<directory>::
+	The repository to get a tar archive from.
+
+Author
+------
+Written by Franck Bui-Huu.
+
+Documentation
+--------------
+Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
+
+GIT
+---
+Part of the gitlink:git[7] suite