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/telegram/message/entity/token.go

@@ -0,0 +1,48 @@
+package entity
+
+// Token represents raw point in a message string.
+type Token struct {
+	utf8offset  int
+	utf16offset int
+}
+
+// UTF8Offset return UTF-8 offset.
+func (t Token) UTF8Offset() int {
+	return t.utf8offset
+}
+
+// UTF16Offset returns UTF-16 offset.
+func (t Token) UTF16Offset() int {
+	return t.utf16offset
+}
+
+// UTF8Length return UTF-8 length between token start and current state.
+func (t Token) UTF8Length(builder *Builder) int {
+	return builder.UTF8Len() - t.utf8offset
+}
+
+// UTF16Length returns UTF-16 length between token start and current state.
+func (t Token) UTF16Length(builder *Builder) int {
+	return builder.UTF16Len() - t.utf16offset
+}
+
+// Text message string between token start and current state.
+func (t Token) Text(builder *Builder) string {
+	return builder.TextRange(t.utf8offset, builder.UTF8Len())
+}
+
+// Apply formats range between token start and current state using given Formatter slice.
+func (t Token) Apply(builder *Builder, f ...Formatter) {
+	builder.appendEntities(t.utf16offset, t.UTF16Length(builder), utf8entity{
+		offset: t.utf8offset,
+		length: t.UTF8Length(builder),
+	}, f...)
+}
+
+// Token creates new Token.
+func (b *Builder) Token() Token {
+	return Token{
+		utf8offset:  b.UTF8Len(),
+		utf16offset: b.UTF16Len(),
+	}
+}