Go Metrics 1.3.0

• Add WithRate(float64) to the metrics interface and to all clients that implement
  the interface. All metrics calls support sample rates.
  • The LoggerClient:
    • Applies the sample rate when printing log messages. If the rate is 0.1 and you call Incr() ten times, expect about one message to have been printed out.
    • Displays the sample rate for counts if it is not 1.0, e.g: Count foo:0.2 (2 * 0.1) [tag1 tag2]. This shows the sampled value, the passed value, and the sample rate.
    • Gauges, timings, and histograms will show the sample rate, but he value is left unmodified just like the DataDog implementation.
  • The RecorderClient:

    • Records all sample rates for metrics calls in MetricCall.Rate. No calls are excluded from the call list based on the sample rate, and the value recorded is the full value before multiplying by the sample rate.

    • Adds a Rate(float64) query method to filter by sampled metrics.

    • The following should work:

      recorder := metrics.NewRecorderClient().WithTest(t)
      recorder.WithRate(0.1).Count("foo", 5)
      recorder.Expect("foo").Rate(0.1).Value(5)

• Add Colorized() method to LoggerClient, and automatically detect a TTY and enable color when nil is passed to the NewLoggerClient constructor.
• Test with Go 1.10.x.