Make.DisplaySourceInitiate rendering of a progress bar display. Raises Failure if there is already an active progress bar display.
reporters d is the list of initial reporting functions belonging to display d.
Note this list does not include any reporters added during progress bar rendering via add_line.
tick d re-renders the contents of display d without reporting any specific values. This function can be used to update spinners, durations, etc. when there is no actual progress to report.
Add a line to an ongoing display, and get its reporting function. By default, the line is added to the bottom of the display (above = 0); the ~above argument can be passed to add the line above some number of existing lines.