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/tdsync/ready_test.go

@@ -0,0 +1,49 @@
+package tdsync
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestReady(t *testing.T) {
+	r := NewReady()
+
+	wait := make(chan struct{})
+	wg := &sync.WaitGroup{}
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		<-r.Ready()
+		<-r.Ready()
+		close(wait)
+	}()
+
+	// Check that Ready can be called multiple times
+	// from different threads.
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		<-r.Ready()
+		<-r.Ready()
+	}()
+
+	// Check that Signal can be called multiple times
+	// from different threads.
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		<-wait
+		r.Signal()
+	}()
+
+	// Check Signal call logic.
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		r.Signal()
+		r.Signal()
+		<-wait
+	}()
+
+	wg.Wait()
+}