Author: Jonas Malaco
    Merge #376: core: make Device hashable again
    

Author: Nick Bogdanov
    Make Device hashable again
    
    Commit 251dbc15df00b5 ("core: implement Device.__eq__") had the side
    effect of making Device objects unhashable, so they could no longer be
    included in a set().  This was a regression from v1.1.1.  Add a
    corresponding __hash__() method so that Device objects are hashable
    again.
    
    Fixes eblot/pyftdi#256
