Pystorm

This release makes `msgpack` an optional requirement, since hardly anyone uses the msgpack serializer. This should solve the issues raised in (50 and 51).

- `ReliableSpout` now inherits from `Spout` as it should (issue 49)

This release fixes an issue where sometimes hung threads would not be killed when a `Component` exits on an exception. (PR 47)

This bugfix release fixes an issue where importing anything from `pystorm` would cause crashes on Windows (Issue 40)

Features
- Added a `ReliableSpout` implementation that can be used to have spouts that will automatically replay failed tuples up to a specified number of times before giving up on them. (PR 39)
- Added `Spout.activate` and `Spout.deactivate` methods that will be called in Storm 1.1.0 and above when a spout is activated or deactivated. This is handy if you want to close database connections on deactivation and reconnect on activation. (Issue 41, PR 42)

Fixes
- Fixed an issue where batching bolts would fail all batches they had received when they encountered an exception, even when `exit_on_exception` was `False`. Now they will only fail the current batch when `exit_on_exception` is `False`; if it is `True`, all batches are still failed. (PR 43)

This bugfix release fixes an issue where a nested exception could still cause a `StormWentAwayError` to be raised (instead of logged). 38