New DNS provider PowerDNS (#748)

* Added PowerDNS as dns provider

* Remove unnecessary comments

* Some tests

* Implemented feedback

vendor/github.com/mittwald/go-powerdns/pdnshttp/req_opt.go

@@ -0,0 +1,58 @@
+package pdnshttp
+
+import (
+	"bytes"
+	"encoding/json"
+	"io"
+	"io/ioutil"
+	"net/http"
+)
+
+// RequestOption is a special type of function that can be passed to most HTTP
+// request functions in this package; it is used to modify an HTTP request and
+// to implement special request logic.
+type RequestOption func(*http.Request) error
+
+// WithJSONRequestBody adds a JSON body to a request. The input type can be
+// anything, as long as it can be marshaled by "json.Marshal". This method will
+// also automatically set the correct content type and content-length.
+func WithJSONRequestBody(in interface{}) RequestOption {
+	return func(req *http.Request) error {
+		if in == nil {
+			return nil
+		}
+
+		buf := bytes.Buffer{}
+		enc := json.NewEncoder(&buf)
+		err := enc.Encode(in)
+
+		if err != nil {
+			return err
+		}
+
+		rc := ioutil.NopCloser(&buf)
+
+		copyBuf := buf.Bytes()
+
+		req.Body = rc
+		req.Header.Set("Content-Type", "application/json")
+		req.ContentLength = int64(buf.Len())
+		req.GetBody = func() (io.ReadCloser, error) {
+			r := bytes.NewReader(copyBuf)
+			return ioutil.NopCloser(r), nil
+		}
+
+		return nil
+	}
+}
+
+// WithQueryValue adds a query parameter to a request's URL.
+func WithQueryValue(key, value string) RequestOption {
+	return func(req *http.Request) error {
+		q := req.URL.Query()
+		q.Set(key, value)
+
+		req.URL.RawQuery = q.Encode()
+		return nil
+	}
+}