Renamed module from riemann to riemann_client
Refactored command line parser to work better with subcommands

Environment variable support is now part of the command line tool only,
not the library itself.
TCPTransport.send returns Riemanns response

UDPTransport.send returns NotImplemented
Version 3.0.0

* Updated documentation
* Removed beta classifier
* Removed riemann-client-<python-version> executable