Improvements to the test suite:
* List release version names and numbers in minecraft/__init__.py.
* Make some tests, which previously ran for *all* protocol versions,
run only for release protocol versions (to improve test performance).
* Make some tests, which previously ran only for the latest protocol
version, run for all release protocol versions (to improve coverage).
* Print each protocol version being tested to the debug log, to help
identify sources of errors.
* Use the `nose-timer' plugin to show the run time of each test.
Fix errors revealed by increased test coverage:
* Fix: SoundEffectPacket.Pitch is not serialised correctly for early
protocol versions.
* Fix: handleExceptionTest finishes later than necessary because
the test overrode an exception handler used internally by
`_FakeServerTest', causing the server thread to time out after 4s.
* Add support for multiple exception handlers in `Connection'
(required for the above).
Improvements to data descriptors:
* Make syntax of property declarations more consistent/Pythonic.
* Factor the definition of several aliasing properties into the
utility methods `attribute_alias' and `multi_attribute_alias',
which construct suitable data descriptors.
* Define and use the named tuple `Direction' for (pitch, yaw) values.
