move gotd fork into repo. (#111)

- update to latest telegram layer
- remove some references to fields in tg.Entities that don't exist in
the schema
- originally added here:
https://github.com/beeper/td/commit/820929062a2ba0104397bc01235ab58a9cff780e
  - referenced here
-
https://github.com/mautrix/telegramgo/commit/124f0967ed195b5a380c9bd02e170ada9710dde3
-
https://github.com/mautrix/telegramgo/commit/4205047aab2e0639217148b5d125bfaab668bd8e

pkg/gotd/cmd/dlkey/main.go

@@ -0,0 +1,59 @@
+// Binary dlkey extracts public keys from remote repo.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"os"
+	"path"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/keyparser"
+)
+
+func main() {
+	var (
+		name   = flag.String("f", "mtproto_dc_options.cpp", "file name to download")
+		base   = flag.String("base", "https://raw.githubusercontent.com/telegramdesktop/tdesktop", "base url")
+		branch = flag.String("branch", "dev", "branch to use")
+		dir    = flag.String("dir", "Telegram/SourceFiles/mtproto/", "directory")
+		out    = flag.String("o", "", "output file name (blank to stdout)")
+	)
+	flag.Parse()
+
+	u, err := url.Parse(*base)
+	if err != nil {
+		panic(err)
+	}
+
+	u.Path = path.Join(u.Path, *branch, *dir, *name)
+
+	res, err := http.Get(u.String())
+	if err != nil {
+		panic(err)
+	}
+	defer func() { _ = res.Body.Close() }()
+	if res.StatusCode/100 != 2 {
+		panic(fmt.Sprintf("status code %d", res.StatusCode))
+	}
+
+	var outWriter io.Writer = os.Stdout
+	if *out != "" {
+		w, err := os.Create(*out)
+		if err != nil {
+			panic(err)
+		}
+		defer func() {
+			if err := w.Close(); err != nil {
+				panic(err)
+			}
+		}()
+		outWriter = w
+	}
+
+	if err := keyparser.Extract(res.Body, outWriter); err != nil {
+		panic(err)
+	}
+}