def __init__(self, dest=None):
self.out = BytesIO() if dest is None else dest<EOL>self.bits = []<EOL>self.bitcount = <NUM_LIT:0><EOL>
dest may be a file-type object (with a write() method).  If None
        then a BytesIO is created, and the contents can be accessed with
        this class's getvalue() method.