tests: Use assertRaises more
futures: set() accepts a function to be called on get()
futures: Add filter(), join(), map(), reduce()
Bump version number to v1.2.0a1
futures: Replace set(callback=...) with set_callback(...)
Remove pylint exceptions
Update URL to gevent tarball
Refactor tests
tox config: Install gevent for Python 2.6 as well
Add eventlet support
travis: Add Python 3.3 build
Merge remote-tracking branch 'jstasiak/eventlet' into develop
eventlet: README tweaks
eventlet: flake8 and style fixes
eventlet: Add support for future callbacks
docs: Add eventlet support to changelog
Refactor replying to messages and add some documentation

This is directly related to #22
docs: Tweak README

- Minor tweaks to new sections on replying from actors.
- Avoid Sphinx syntax in the README, as it should work perfectly on GitHub and
  PyPI in addition to pykka.org.
docs: Update changelog
Reply to messages left in actor inbox after it's stopped