Initial sphinx/readthedocs documentation (closes #11)
Documented riemann_client.client module, minor code changes

* QueuedClient correctly overrides both send_event() and send_events()
* QueuedClient send_event() and send_events() both return None
* QueuedClient flush() now returns the recived message
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Documented riemann_client.transport module
Fixed links in README.rst
Clearer changelog for CLI changes
UDPTransport.send() returns None instead of NotImplemented (thanks @jonparish)
Fixed minor spelling mistake in docs (thanks @jonparish)
Fixed QueuedClient.send_event
Update outdated text in README
Release version 5