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/fields.go

@@ -0,0 +1,49 @@
+package bin
+
+import "strconv"
+
+// Fields represent a bitfield value that compactly encodes
+// information about provided conditional fields, e.g. says
+// that fields "1", "5" and "10" were set.
+type Fields uint32
+
+// Zero returns true, if all bits are equal to zero.
+func (f Fields) Zero() bool {
+	return f == 0
+}
+
+// String implement fmt.Stringer
+func (f Fields) String() string {
+	return strconv.FormatUint(uint64(f), 2)
+}
+
+// Decode implements Decoder.
+func (f *Fields) Decode(b *Buffer) error {
+	v, err := b.Int32()
+	if err != nil {
+		return err
+	}
+	*f = Fields(v)
+	return nil
+}
+
+// Encode implements Encoder.
+func (f Fields) Encode(b *Buffer) error {
+	b.PutUint32(uint32(f))
+	return nil
+}
+
+// Has reports whether field with index n was set.
+func (f Fields) Has(n int) bool {
+	return f&(1<<n) != 0
+}
+
+// Unset unsets field with index n.
+func (f *Fields) Unset(n int) {
+	*f &= ^(1 << n)
+}
+
+// Set sets field with index n.
+func (f *Fields) Set(n int) {
+	*f |= 1 << n
+}