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/syncio/reader.go

@@ -0,0 +1,26 @@
+package syncio
+
+import (
+	"io"
+	"sync"
+)
+
+// Reader is synchronized io.Reader.
+type Reader struct {
+	r   io.Reader
+	mux sync.Mutex
+}
+
+// NewReader creates new Reader.
+func NewReader(r io.Reader) *Reader {
+	return &Reader{r: r}
+}
+
+// Read implements io.Reader.
+func (s *Reader) Read(p []byte) (n int, err error) {
+	s.mux.Lock()
+	n, err = s.r.Read(p)
+	s.mux.Unlock()
+
+	return
+}