Access to time elapsed

[EvanSchalton]

Hey, firstly -- great tool! Thank you!

A minor feature request:
It'd be great to add a "runtime" method to the progress bar object

I've been using the following as a work around:

import time
def tqdm_runtime(prog_bar):
    epoch_prog.start_t
    epoch_prog.last_print_t
    return time.strftime('%H:%M:%S', time.gmtime(epoch_prog.last_print_t-epoch_prog.start_t))

I use it frequently to log the runtime of training neural nets, but it'd be great to see the method added

[casperdcl]

duplicate of #482, elaborated in #494, enhanced by #562

[casperdcl]

P.S. you can use epoch_prog.format_interval(epoch_prog.last_print_t-epoch_prog.start_t) or just epoch_prog.format_interval(epoch_prog['elapsed'])