Help needed: vendor files for Prometheus support

These are the vendor files needed for Prometheus support.
I have not been able to figure out how to do this properly with gopkg.

vendor/github.com/miolini/datacounter/README.md

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+# datacounter
+Golang counters for readers/writers
+
+[![Build Status](https://travis-ci.org/miolini/datacounter.svg)](https://travis-ci.org/miolini/datacounter) [![GoDoc](https://godoc.org/github.com/miolini/datacounter?status.svg)](http://godoc.org/github.com/miolini/datacounter) [![Go Report Card](http://goreportcard.com/badge/miolini/datacounter)](http://goreportcard.com/report/miolini/datacounter)
+
+## Examples 
+### ReaderCounter
+```go
+buf := bytes.Buffer{}
+buf.Write(data)
+counter := datacounter.NewReaderCounter(&buf)
+io.Copy(ioutil.Discard, counter)
+if counter.Count() != dataLen {
+	t.Fatalf("count mismatch len of test data: %d != %d", counter.Count(), len(data))
+}`
+```
+### WriterCounter
+```go
+buf := bytes.Buffer{}
+counter := datacounter.NewWriterCounter(&buf)
+counter.Write(data)
+if counter.Count() != dataLen {
+	t.Fatalf("count mismatch len of test data: %d != %d", counter.Count(), len(data))
+}
+```
+### http.ResponseWriter Counter
+```go
+handler := func(w http.ResponseWriter, r *http.Request) {
+	w.Write(data)
+}
+req, err := http.NewRequest("GET", "http://example.com/foo", nil)
+if err != nil {
+	t.Fatal(err)
+}
+w := httptest.NewRecorder()
+counter := datacounter.NewResponseWriterCounter(w)
+handler(counter, req)
+if counter.Count() != dataLen {
+	t.Fatalf("count mismatch len of test data: %d != %d", counter.Count(), len(data))
+}
+```