Process a line of user input and use callback functions dir-fns, which is a map of functions that are called by key based on the following actions:

• :end-query called when the user is completed her input and wants to send it to be processed
• :end-session the user has given the exit command
• :end-file the user has hit the end of file sequence (CTRL-D)

Start the command event loop using standard in/out.