'Returns a new :class:`Arrow <arrow.arrow.Arrow>` object, representing the "floor"
of the timespan of the :class:`Arrow <arrow.arrow.Arrow>` object in a given timeframe.
Equivalent to the first element in the 2-tuple returned by
:func:`span <arrow.arrow.Arrow.span>`.
:param frame: the timeframe.  Can be any ``datetime`` property (day, hour, minute...).
Usage::
>>> arrow.utcnow().floor(\'hour\')
<Arrow [2013-05-09T03:00:00+00:00]>'

def floor(self, frame):

    return self.span(frame)[0]
