Stop operation

Sometimes when you need to run **acceptance tests** automatically through the CI process (e.g. [Travis-CI](https://travis-ci.org)), you'd need to start the server, run your end-to-end tests and then stop the server. This pull request aims to add a **stop** operation to allow the instantiated spawned server to stop and move on.

Note: I notice you still don't have unit/integration tests on your repository. If you accept this pull request a can help to write some tests if you want me to.