CloudFormation template for managing the project's AWS CodeBuild work…

…flows (awslabs#159)

* CloudFormation template to model the AWS Code Build resources

to help maintainers with adding/modifying the CI workflows

also adds helper script `ci/update-images.sh` for re-building and re-uploading the `ci/docker/*` images

* fix dockerfile name in update-images

ci/README.md

@@ -0,0 +1,14 @@
+## AWS CodeBuild Stack Setup
+
+create or update the stack
+```
+aws cloudformation deploy --capabilities CAPABILITY_IAM --stack-name aws-lambda-cpp-ci --template-file codebuild.yml
+```
+
+(optional) trigger docker build and docker push of the build environment images.
+A project to do this is pre-configured in the deployed stack.
+```
+aws cloudformation describe-stacks --stack-name aws-lambda-cpp-ci --query "Stacks[].Outputs[].OutputValue"
+# run command output from above, will look like:
+# aws codebuild start-build --project-name <value>
+```