Release 0.9.0

Bugfixes:

  - 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

New Features:

  - Report an error for 'return' outside a function

I'd like to thank all the people who contributed to this release:

  - Aaron Meurer
  - Adi Roiban
  - Charles-Francois Natali
  - Florent Xicluna
  - Ian Cordasco
  - Jan Stürtz
  - ryneeverett
  - Steven Myint