v5.0.0

• Add Tag support: suffix-octothorpe, infix-comma, infix-semicolon (GH-53)
• Remove previously deprecated NoopClient. Use a nil *Client Statter as a
  replacement, if needed. Ex:

  var client Client
  // A nil *Client has noop behavior, so this is safe.
  // It will become a small overhead (just a couple function calls) noop.
  err = client.Inc("stat1", 42, 1.0)