Added a progress bar after feedback during the recent SFU tutorial.
The current bar progresses every 2.5 % and prints the percentage every 20 %.
It is only active if the number of iterations are greater than 100, and the new Output section option print_progress_bar is set to true (or on, yes, 1 as usual). The default value is true, so only need to set it to false if a progress bar is not desired.