Pyflakes

- Python 3.5 support. async/await statements in particular.
- Fix test_api.py on Windows.
- Eliminate a false UnusedImport warning when the name has been
declared "global"

- Fix a traceback when a global is defined in one scope, and used in another.

- Update NEWS.txt to include 0.9.0, which had been forgotten.

- Exit gracefully, not with a traceback, on SIGINT and SIGPIPE.
- Fix incorrect report of undefined name when using lambda expressions in
generator expressions.
- Don't crash on DOS line endings on Windows and Python 2.6.
- Don't report an undefined name if the 'del' which caused a name to become
undefined is only conditionally executed.
- Properly handle differences in list comprehension scope in Python 3.
- Improve handling of edge cases around 'global' defined variables.
- Report an error for 'return' outside a function.

- Detect the declared encoding in Python 3.
- Do not report redefinition of import in a local scope, if the
global name is used elsewhere in the module.
- Catch undefined variable in loop generator when it is also used as
loop variable.
- Report undefined name for ``(a, b) = (1, 2)`` but not for the general
unpacking ``(a, b) = func()``.
- Correctly detect when an imported module is used in default arguments
of a method, when the method and the module use the same name.
- Distribute a universal wheel file.

- Adapt for the AST in Python 3.4.
- Fix caret position on SyntaxError.
- Fix crash on Python 2.x with some doctest SyntaxError.
- Add tox.ini.
- The ``PYFLAKES_NODOCTEST`` environment variable has been replaced with the
``PYFLAKES_DOCTEST`` environment variable (with the opposite meaning).
Doctest checking is now disabled by default; set the environment variable
to enable it.
- Correctly parse incremental ``__all__ += [...]``.
- Catch return with arguments inside a generator (Python <= 3.2).
- Do not complain about ``_`` in doctests.
- Drop deprecated methods ``pushFunctionScope`` and ``pushClassScope``.