Use Circle CI for faster builds. (#181)

Move to Circle CI from Travis CI.

setup_env.sh

@@ -0,0 +1,38 @@
+# Script to setup environment variables.
+
+set -ex
+
+set_var () {
+	echo $1=$2 >> $BASH_ENV
+	export $1=$2
+}
+
+setup_env () {
+	CI_NAME=$1
+	# Set the current branch name.
+	BRANCH_NAME=${CI_NAME}_BRANCH
+    set_var BRANCH ${!BRANCH_NAME}
+}
+
+
+if [ "$TRAVIS" ]; then
+	# Set environments picked up from Circle CI.
+	set_var EVENT_TYPE "$TRAVIS_EVENT_TYPE"
+	set_var COMMIT_ID $TRAVIS_COMMIT
+	# Setup some generic environment vars.
+	setup_env TRAVIS
+elif [ "$CIRCLECI" ]; then
+	# Set environments picked up from Circle CI.
+	set_var EVENT_TYPE "push"
+	set_var COMMIT_ID $CIRCLE_SHA1
+	# Setup some generic environment vars.
+	setup_env CIRCLE
+fi
+
+if [ "$BRANCH" = "master" ]; then
+	set_var TAG "latest"
+else
+	set_var TAG "$BRANCH"
+fi
+
+set_var REG_URL ${REGISTRY}_URL