contrib: move "update-unicode.sh" script into "tools/"

The "update-unicode.sh" script is used to update the unicode data
compiled into Git whenever a new version of the Unicode standard has
been released. As such, it is a natural part of our developer-facing
tooling, and its presence in "contrib/" is misleading.

Promote the script into the new "tools/" directory.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/contrib/update-unicode/.gitignore b/tools/update-unicode/.gitignore
similarity index 100%
rename from contrib/update-unicode/.gitignore
rename to tools/update-unicode/.gitignore

diff --git a/contrib/update-unicode/README b/tools/update-unicode/README
similarity index 100%
rename from contrib/update-unicode/README
rename to tools/update-unicode/README

diff --git a/contrib/update-unicode/update_unicode.sh b/tools/update-unicode/update_unicode.sh
similarity index 100%
rename from contrib/update-unicode/update_unicode.sh
rename to tools/update-unicode/update_unicode.sh