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/crypto/session_id_test.go

@@ -0,0 +1,25 @@
+package crypto
+
+import (
+	"crypto/rand"
+	mathrand "math/rand"
+	"testing"
+)
+
+func TestNewSessionID(t *testing.T) {
+	t.Run("Crypto", func(t *testing.T) {
+		if _, err := NewSessionID(rand.Reader); err != nil {
+			t.Fatal(err)
+		}
+	})
+	t.Run("Math", func(t *testing.T) {
+		rnd := mathrand.New(mathrand.NewSource(239))
+		n, err := NewSessionID(rnd)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if n != 2092333242585417206 {
+			t.Fatal("mismatch")
+		}
+	})
+}