flake8 fixes

Added str type as alias for missing unicode type in python3.  Replace
type(x) == type(y) with isinstance(x, (type_of_y, or other type))
which is usually str or unicode (hence need for unicode def).

Used De Morgan's to convert things like:

  type(value) != type('') and type(value) != type(u'')

into

  not isinstance(value, (str, unicode))

a couple of variable name replacements.

Author: rouilj