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/gen/_template/string.tmpl

@@ -0,0 +1,10 @@
+{{define "string_derive" }}{{ $s := $ }}
+// String implements fmt.Stringer.
+func ({{ $s.Receiver }} *{{ $s.Name }}) String() string {
+    if {{ $s.Receiver }} == nil {
+        return "{{ $.Name }}(nil)"
+    }
+    type Alias {{ $s.Name }}
+    return fmt.Sprintf("{{ $s.Name }}%+v", Alias(*{{ $s.Receiver }}))
+}
+{{- end }}