In the parse routine, collapsed the 'pfm', 'sites' and 'jaspar' into one elif
as they are now called and returned the same way.
Refactored read routine into three different private routines for reading
each of the three format types. The main read routine calls one of the three
specific read routines depending on the format type passed into it.

Fixed __init__ method to work when motif is initialized from instances instead
of counts.