CLN: fix all flake8 warnings in pandas/io
I suppressed warnings in test_parsers.py because of the amount of literal strings in the file. 

@jreback can you give me a thumbs up to merge if the build passes? 
 or @jorisvandenbossche too. Nested lists in RST I think require the extra line break
 some minor comments. only issue is maybe we shouldn't touch.

`io/data.py`, `io/wb.py` & `io/ga.py` (and associated tests) and just put `no qa` at the top as these are deprecated.
 I see; any harm in leaving them as is here or would you prefer I revert the changes? 
 in theory your changes should be fine for `io/data.y` & `io/wb.py` (except for sure revert the `ga` as those tests have not been run for quite some time and are essentially disabled).

just trying not to touch those until they are removed.
 @jreback I think we are not going to updat the ´io/data.py´ code anymore with changes that happen in pandas-datareader? (as we did in the beginning) If that is the case, I don't think there is any harm in leaving that file in here, otherwise I would say to revert (to more easily compare/update with pandas-datareader)
 @jorisvandenbossche no it won't be updated. Just trying to not change it. These pep changes won't hurt,  as they are tested, so really no big deal. (bigger deal is `ga.py` which in theory should still work as hasn't been touched).
 OK, I unstaged the ga/wb/data changes and cleaned up the parse_dates bit of the docstring. Will merge once the build passes
