Runs the actual command loop, providing readline output via rustyline.
The context arg allows for the passing of additional ‘context’ information
to maintain a state during subcalls if needed.
Sets the cursor location to the bottom-most row and the column to 1.
This gets run automatically in command_loop().
This function will print a line to the screen, one line above the
bottom-most row of the terminal.
Optionally, a prefix can be provided in case you would like to add
additional context to the output line.