Add basic Graphite protocol reader.

I've implemented a reader for Graphite's TCP protocol;

    s, _ := net.Listen("tcp", 2003)
    out := make(chan *metrics.Metric, SOME_BUFFER_SIZE)
    for {
        c, _ := server.Accept()
        go GraphiteProtocolReader(c, out)
    }

I couldn't quite figure out where to hook it up though. Give me a ping about where to look, and I'll take a stab at it.