apply autopep8 standards.

$ flake8 rdflib --exclude=pyRdfa,host,extras,transform,rdfs,pyMicrodata
rdflib/graph.py:192: W801 redefinition of unused 'BytesIO' from line 189
rdflib/graph.py:194: W402 'BytesIO' imported but unused
rdflib/graph.py:680:80: E501 line too long (80 > 79 characters)
rdflib/graph.py:682:80: E501 line too long (80 > 79 characters)
rdflib/graph.py:686:80: E501 line too long (83 > 79 characters)
rdflib/graph.py:690:80: E501 line too long (83 > 79 characters)
rdflib/graph.py:692:80: E501 line too long (83 > 79 characters)
rdflib/graph.py:695:80: E501 line too long (83 > 79 characters)
rdflib/graph.py:698:80: E501 line too long (83 > 79 characters)
rdflib/parser.py:21: W801 redefinition of unused 'BytesIO' from line 19
rdflib/compat.py:12: W801 redefinition of unused 'defaultdict' from line 10
rdflib/py3compat.py:10: W801 redefinition of unused 'wraps' from line 7
rdflib/py3compat.py:81: W806 redefinition of function 'b' from line 44
rdflib/py3compat.py:87: W806 redefinition of function 'format_doctest_out' from line 50
rdflib/py3compat.py:97: W806 redefinition of function 'type_cmp' from line 61
rdflib/term.py:54: W801 redefinition of unused 'md5' from line 52
rdflib/store.py:73: W801 redefinition of unused 'BytesIO' from line 71
rdflib/query.py:10: W801 redefinition of unused 'BytesIO' from line 8
rdflib/__init__.py:73: W402 'plugin' imported but unused
rdflib/__init__.py:74: W402 'query' imported but unused
rdflib/util.py:43: W806 redefinition of function 'sign' from line 50
rdflib/plugins/parsers/hturtle.py:25: W801 redefinition of unused 'html5lib' from line 24
rdflib/plugins/parsers/ntriples.py:141: W402 'BytesIO' imported but unused
rdflib/plugins/parsers/structureddata.py:23: W801 redefinition of unused 'html5lib' from line 22