Add go-charset and chardet to vendor

vendor/github.com/paulrosania/go-charset/charset/utf8.go

@@ -0,0 +1,51 @@
+package charset
+
+import (
+	"unicode/utf8"
+)
+
+func init() {
+	registerClass("utf8", toUTF8, toUTF8)
+}
+
+type translateToUTF8 struct {
+	scratch []byte
+}
+
+var errorBytes = []byte(string(utf8.RuneError))
+
+const errorRuneLen = len(string(utf8.RuneError))
+
+func (p *translateToUTF8) Translate(data []byte, eof bool) (int, []byte, error) {
+	p.scratch = ensureCap(p.scratch, (len(data))*errorRuneLen)
+	buf := p.scratch[:0]
+	for i := 0; i < len(data); {
+		// fast path for ASCII
+		if b := data[i]; b < utf8.RuneSelf {
+			buf = append(buf, b)
+			i++
+			continue
+		}
+		_, size := utf8.DecodeRune(data[i:])
+		if size == 1 {
+			if !eof && !utf8.FullRune(data) {
+				// When DecodeRune has converted only a single
+				// byte, we know there must be some kind of error
+				// because we know the byte's not ASCII.
+				// If we aren't at EOF, and it's an incomplete
+				// rune encoding, then we return to process
+				// the final bytes in a subsequent call.
+				return i, buf, nil
+			}
+			buf = append(buf, errorBytes...)
+		} else {
+			buf = append(buf, data[i:i+size]...)
+		}
+		i += size
+	}
+	return len(data), buf, nil
+}
+
+func toUTF8(arg string) (Translator, error) {
+	return new(translateToUTF8), nil
+}