CI: Add .gitlab-ci.yml to start using CI.

.gitlab-ci.yml

+# This file is a template, and might need editing before it works on your project.
+# Official language image. Look for the different tagged releases at:
+# https://hub.docker.com/r/library/rust/tags/
+image: "rust:latest"
+
+# Optional: Pick zero or more services to be used on all builds.
+# Only needed when using a docker container to run your tests in.
+# Check out: http://docs.gitlab.com/ce/ci/docker/using_docker_images.html#what-is-a-service
+# services:
+#   - mysql:latest
+#   - redis:latest
+#   - postgres:latest
+
+# Optional: Install a C compiler, cmake and git into the container.
+# You will often need this when you (or any of your dependencies) depends on C code.
+# before_script:
+#   - apt-get update -yqq
+#   - apt-get install -yqq --no-install-recommends build-essential
+
+# Use cargo to test the project
+test:cargo:
+  script:
+    - rustc --version && cargo --version  # Print version info for debugging
+    - cargo test --all --verbose