'shift(hours, minutes, seconds, milliseconds, ratio)
Shift `start` and `end` attributes of each items of file either by
applying a ratio or by adding an offset.
`ratio` should be either an int or a float.
Example to convert subtitles from 23.9 fps to 25 fps:
>>> subs.shift(ratio=25/23.9)
All "time" arguments are optional and have a default value of 0.
Example to delay all subs from 2 seconds and half
>>> subs.shift(seconds=2, milliseconds=500)'

def shift(self, *args, **kwargs):

    for item in self:
        item.shift(*args, **kwargs)
