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/gen/doc.go

@@ -0,0 +1,63 @@
+// Package gen implements code generation from TL schema.
+package gen
+
+import (
+	"net/url"
+	"path"
+	"strings"
+	"unicode"
+)
+
+func cloneURL(u *url.URL) *url.URL {
+	if u == nil {
+		return nil
+	}
+	u2 := new(url.URL)
+	*u2 = *u
+	if u.User != nil {
+		u2.User = new(url.Userinfo)
+		*u2.User = *u.User
+	}
+	return u2
+}
+
+func (g *Generator) docURL(parts ...string) string {
+	if g.docBase == nil {
+		return ""
+	}
+
+	u := cloneURL(g.docBase)
+	u.Path = path.Join(append([]string{u.Path}, parts...)...)
+
+	return u.String()
+}
+
+func splitLine(s string, limit int) (r []string) {
+	for {
+		if len(s) < limit {
+			r = append(r, s)
+			return
+		}
+
+		idx := strings.LastIndexFunc(s[:limit], func(r rune) bool {
+			return unicode.IsSpace(r) || r == '.' || r == ','
+		})
+		if idx < 0 || len(s)-1 == idx {
+			r = append(r, s)
+			return
+		}
+
+		r = append(r, s[:idx])
+		s = s[idx+1:]
+	}
+}
+
+func splitLines(s []string, limit int) []string {
+	r := make([]string, 0, len(s))
+
+	for _, line := range s {
+		r = append(r, splitLine(line, limit)...)
+	}
+
+	return r
+}