add file link support

bof.go

@@ -1,12 +1,30 @@
 package xls
 
-import ()
+import (
+	"bytes"
+	"encoding/binary"
+	"io"
+	"unicode/utf16"
+)
 
 type BOF struct {
 	Id   uint16
 	Size uint16
 }
 
+func (b *BOF) Reader(buf io.ReadSeeker) io.ReadSeeker {
+	rts := make([]byte, b.Size)
+	buf.Read(rts)
+	return bytes.NewReader(rts)
+}
+
+func (b *BOF) Utf16String(buf io.ReadSeeker, count uint32) string {
+	var bts = make([]uint16, count)
+	binary.Read(buf, binary.LittleEndian, &bts)
+	runes := utf16.Decode(bts[:len(bts)-1])
+	return string(runes)
+}
+
 type BIFFHeader struct {
 	Ver     uint16
 	Type    uint16