Update variables for managing a server's child processes.
Add shell utilities for server connections and printing the Impromptu environment.
Add CLI commands to start and shut down the server.
Always check if the server's pid file exists before pinging the server.
Shut down the Redis server after all tests have completed.
Improve server commands. Allow the server to run in the foreground.

* Run the server in the foreground with `impromptu server start --foreground`.
* Improves the server's safe shutdown by waiting for all connections to complete before terminating.
* Adds a utility for pinging the server.
Add a command to kill all impromptu-related processes.

Kill all impromptu-related processes with `impromptu kill`.
Handle Ctrl+C and PID file management in the node server.