Enhancements on indentation for lines after a backslash continuation.

Enhancements on indentation for lines after a backslash continuation.

Backslashed continuations with parens in the middle are now handled
correctly. Things like this are now indented properly:

objects = Thing.objects.all() \
                       .filter(
                           type="toy",
                           status="bought"
                           subtype="car"
                       ) \
                       .aggregate(
                           Sum('amount')
                       ) \
                       .values_list()

New Functions:

    * `python-info-beginning-of-backlash' returns the point where a
      backslashed line start.