Move util/ to tools/

GitHub ignores the contents of the tools/ directory for the purpose of
repo language statistics.

.gitattributes

@@ -3,4 +3,4 @@
 /.travis.yml      export-ignore
 /phpunit.xml.dist export-ignore
 /tests            export-ignore
-/util             export-ignore
+/tools            export-ignore

CONTRIBUTING.md

@@ -60,7 +60,7 @@ composer test
 
 ### Locally Test With Emulated MIPS Architecture
 
-The following commands use [Vagrant](https://www.vagrantup.com/) to start an Ubuntu VM, install necessary dependencies, and then run the `util/run-tests.sh` script that will download a Docker image emulating the MIPS architecture. This is especially helpful for testing UUID generation in a big-endian environment.
+The following commands use [Vagrant](https://www.vagrantup.com/) to start an Ubuntu VM, install necessary dependencies, and then run the `tools/run-tests.sh` script that will download a Docker image emulating the MIPS architecture. This is especially helpful for testing UUID generation in a big-endian environment.
 
 ```
 vagrant init ubuntu/trusty64
@@ -71,5 +71,5 @@ cd /vagrant
 curl -sS https://getcomposer.org/installer | php
 php composer.phar install --no-interaction --prefer-dist
 mkdir -p build/logs
-ARCH=mips PHP_VERSION=5.6.14 TRAVIS_BUILD_DIR=/vagrant ./util/run-tests.sh
+ARCH=mips PHP_VERSION=5.6.14 TRAVIS_BUILD_DIR=/vagrant ./tools/run-tests.sh
 ```

tools/build-docker-image.sh

@@ -17,11 +17,11 @@
 #     sudo apt-get install docker.io
 #     sudo docker login
 #     cd /vagrant
-#     sudo ./util/build-docker-image.sh 5.6.14 mips mips wheezy
+#     sudo ./tools/build-docker-image.sh 5.6.14 mips mips wheezy
 #
 # or (for 64-bit, standard Debian):
 #
-#     sudo ./util/build-docker-image.sh 5.6.14 x86_64 amd64 wheezy
+#     sudo ./tools/build-docker-image.sh 5.6.14 x86_64 amd64 wheezy
 #
 
 if [ $EUID -ne 0 ]; then