Add go-charset and chardet to vendor

vendor/github.com/paulrosania/go-charset/charset/big5.go

@@ -0,0 +1,88 @@
+package charset
+
+import (
+	"fmt"
+	"unicode/utf8"
+)
+
+func init() {
+	registerClass("big5", fromBig5, nil)
+}
+
+// Big5 consists of 89 fonts of 157 chars each
+const (
+	big5Max  = 13973
+	big5Font = 157
+	big5Data = "big5.dat"
+)
+
+type translateFromBig5 struct {
+	font    int
+	scratch []byte
+	big5map []rune
+}
+
+func (p *translateFromBig5) Translate(data []byte, eof bool) (int, []byte, error) {
+	p.scratch = p.scratch[:0]
+	n := 0
+	for len(data) > 0 {
+		c := int(data[0])
+		data = data[1:]
+		n++
+		if p.font == -1 {
+			// idle state
+			if c >= 0xa1 {
+				p.font = c
+				continue
+			}
+			if c == 26 {
+				c = '\n'
+			}
+			continue
+		}
+		f := p.font
+		p.font = -1
+		r := utf8.RuneError
+		switch {
+		case c >= 64 && c <= 126:
+			c -= 64
+		case c >= 161 && c <= 254:
+			c = c - 161 + 63
+		default:
+			// bad big5 char
+			f = 255
+		}
+		if f <= 254 {
+			f -= 161
+			ix := f*big5Font + c
+			if ix < len(p.big5map) {
+				r = p.big5map[ix]
+			}
+			if r == -1 {
+				r = utf8.RuneError
+			}
+		}
+		p.scratch = appendRune(p.scratch, r)
+	}
+	return n, p.scratch, nil
+}
+
+type big5Key bool
+
+func fromBig5(arg string) (Translator, error) {
+	big5map, err := cache(big5Key(false), func() (interface{}, error) {
+		data, err := readFile(big5Data)
+		if err != nil {
+			return nil, fmt.Errorf("charset: cannot open big5 data file: %v", err)
+		}
+		big5map := []rune(string(data))
+		if len(big5map) != big5Max {
+			return nil, fmt.Errorf("charset: corrupt big5 data")
+		}
+		return big5map, nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return &translateFromBig5{big5map: big5map.([]rune), font: -1}, nil
+}