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/telegram/updates/gap_check.go

@@ -0,0 +1,27 @@
+package updates
+
+type gapCheckResult byte
+
+const (
+	_ gapCheckResult = iota
+	gapApply
+	gapIgnore
+	gapRefetch
+)
+
+func checkGap(localState, remoteState, count int) gapCheckResult {
+	// Temporary fix for handling qts updates gaps.
+	if remoteState == 0 {
+		return gapApply
+	}
+
+	if localState+count == remoteState {
+		return gapApply
+	}
+
+	if localState+count > remoteState {
+		return gapIgnore
+	}
+
+	return gapRefetch
+}