Add Bundler and Rake tasks

Uses Bundler for dependency management and Rake for calling methods on the `jently_control.rb` file. Rake is a common interface to shell scripts in most Ruby apps, so it will be familiar to Rubyists. The `rake` base task will determine whether a PID file exists or not, and if it does, it will assume the server is running and stop it. Otherwise, `rake` starts the server.