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/clock/clock.go

@@ -0,0 +1,31 @@
+// Package clock abstracts time source.
+package clock
+
+import (
+	"time"
+
+	"github.com/gotd/neo"
+)
+
+// Clock is current time source.
+type Clock interface {
+	Now() time.Time
+	Timer(d time.Duration) Timer
+	Ticker(d time.Duration) Ticker
+}
+
+// Timer abstracts a single event.
+type Timer = neo.Timer
+
+// StopTimer stops timer and drains timer channel if Stop() returned false.
+func StopTimer(t Timer) {
+	if !t.Stop() {
+		select {
+		case <-t.C():
+		default:
+		}
+	}
+}
+
+// Ticker abstracts a channel that delivers “ticks” of a clock at intervals.
+type Ticker = neo.Ticker

pkg/gotd/clock/system.go

@@ -0,0 +1,50 @@
+package clock
+
+import "time"
+
+type systemTimer struct {
+	timer *time.Timer
+}
+
+func (s systemTimer) C() <-chan time.Time {
+	return s.timer.C
+}
+
+func (s systemTimer) Reset(d time.Duration) {
+	s.timer.Reset(d)
+}
+
+func (s systemTimer) Stop() bool {
+	return s.timer.Stop()
+}
+
+type systemTicker struct {
+	ticker *time.Ticker
+}
+
+func (s systemTicker) C() <-chan time.Time {
+	return s.ticker.C
+}
+
+func (s systemTicker) Stop() {
+	s.ticker.Stop()
+}
+
+func (s systemTicker) Reset(d time.Duration) {
+	s.ticker.Reset(d)
+}
+
+type systemClock struct{}
+
+func (clock systemClock) Ticker(d time.Duration) Ticker {
+	return systemTicker{ticker: time.NewTicker(d)}
+}
+
+func (systemClock) Timer(d time.Duration) Timer {
+	return systemTimer{timer: time.NewTimer(d)}
+}
+
+func (systemClock) Now() time.Time { return time.Now() }
+
+// System Clock.
+var System Clock = systemClock{}