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/bin/buffer.go

@@ -0,0 +1,71 @@
+package bin
+
+import (
+	"io"
+)
+
+// Buffer implements low level binary (de-)serialization for TL.
+type Buffer struct {
+	Buf []byte
+}
+
+// Encode wrapper.
+func (b *Buffer) Encode(e Encoder) error {
+	return e.Encode(b)
+}
+
+// Decode wrapper.
+func (b *Buffer) Decode(d Decoder) error {
+	return d.Decode(b)
+}
+
+// ResetN resets buffer and expands it to fit n bytes.
+func (b *Buffer) ResetN(n int) {
+	b.Buf = append(b.Buf[:0], make([]byte, n)...)
+}
+
+// Expand expands buffer to add n bytes.
+func (b *Buffer) Expand(n int) {
+	b.Buf = append(b.Buf, make([]byte, n)...)
+}
+
+// Skip moves cursor for next n bytes.
+func (b *Buffer) Skip(n int) {
+	b.Buf = b.Buf[n:]
+}
+
+// Read implements io.Reader.
+func (b *Buffer) Read(p []byte) (n int, err error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+	if len(b.Buf) == 0 {
+		return 0, io.EOF
+	}
+	n = copy(p, b.Buf)
+	b.Buf = b.Buf[n:]
+	return n, nil
+}
+
+// Copy returns new copy of buffer.
+func (b *Buffer) Copy() []byte {
+	return append([]byte{}, b.Buf...)
+}
+
+// Raw returns internal byte slice.
+func (b Buffer) Raw() []byte {
+	return b.Buf
+}
+
+// Len returns length of internal buffer.
+func (b Buffer) Len() int {
+	return len(b.Buf)
+}
+
+// ResetTo sets internal buffer exactly to provided value.
+//
+// Buffer will retain buf, so user should not modify or read it
+// concurrently.
+func (b *Buffer) ResetTo(buf []byte) {
+	b.Buf = buf
+}