Add support for new Comments endpoints (#43)

* Add `Client.CreateComment` method

* Add `Client.FindCommentsByBlockID` method

examples/list-comments/main.go

@@ -0,0 +1,72 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"flag"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/dstotijn/go-notion"
+	"github.com/sanity-io/litter"
+)
+
+type httpTransport struct {
+	w io.Writer
+}
+
+// RoundTrip implements http.RoundTripper. It multiplexes the read HTTP response
+// data to an io.Writer for debugging.
+func (t *httpTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	res, err := http.DefaultTransport.RoundTrip(req)
+	if err != nil {
+		return nil, err
+	}
+
+	res.Body = io.NopCloser(io.TeeReader(res.Body, t.w))
+
+	return res, nil
+}
+
+func main() {
+	ctx := context.Background()
+	apiKey := os.Getenv("NOTION_API_KEY")
+	buf := &bytes.Buffer{}
+	httpClient := &http.Client{
+		Timeout:   10 * time.Second,
+		Transport: &httpTransport{w: buf},
+	}
+	client := notion.NewClient(apiKey, notion.WithHTTPClient(httpClient))
+
+	var blockID string
+
+	flag.StringVar(&blockID, "blockId", "", "Block ID")
+	flag.Parse()
+
+	query := notion.FindCommentsByBlockIDQuery{
+		BlockID: blockID,
+	}
+	resp, err := client.FindCommentsByBlockID(ctx, query)
+	if err != nil {
+		log.Fatalf("Failed to list comments: %v", err)
+	}
+
+	decoded := map[string]interface{}{}
+	if err := json.NewDecoder(buf).Decode(&decoded); err != nil {
+		log.Fatal(err)
+	}
+
+	// Pretty print JSON reponse.
+	enc := json.NewEncoder(os.Stdout)
+	enc.SetIndent("", "    ")
+	if err := enc.Encode(decoded); err != nil {
+		log.Fatal(err)
+	}
+
+	// Pretty print parsed `notion.Comment` value.
+	litter.Dump(resp)
+}