Client Support IPv6 address

[jack-at-circle]

The current New function supports taking an IPv4 address, but not an IPv6 address for initialization i.e.

func TestIPv6(t *testing.T) {
	// passes
	_, err := statsd.New("127.0.0.1")
	assert.NoError(t, err)

	// fails
	_, err = statsd.New("::1")
	assert.NoError(t, err)
}

It would be really nice if the New function would support IPv6 addresses in the same way to make service migrations to IPv6 not require code changes : )