完善gxml中匹配encoding的处理，增加gcharset包的说明

g/encoding/gcharset/gcharset.go

@@ -7,7 +7,8 @@
 //gcharset
 //@author wenzi1
 //@date   20180604
-
+//字符集转换方法.
+//使用mahonia实现的字符集转换方法，支持的字符集包括常见的utf8/UTF-16/UTF-16LE/macintosh/big5/gbk/gb18030,支持的全量字符集可以参考mahonia包
 package gcharset
 
 import (
@@ -16,6 +17,8 @@ import (
 	"fmt"
 )
 
+
+
 //获取支持的字符集
 func GetCharset(name string) (*mahonia.Charset, error) {
 	s := mahonia.GetCharset(name)

g/encoding/gxml/gxml.go

@@ -11,7 +11,7 @@ import (
     "github.com/clbanning/mxj"
     "encoding/xml"
     "io"
-	"gitee.com/johng/gf/g/encoding/gcharset"
+	"gitee.com/wenzi1/gf/g/encoding/gcharset"
 	"gitee.com/johng/gf/g/util/gregx"
 )
 
@@ -45,7 +45,7 @@ func ToJson(xmlbyte []byte) ([]byte, error) {
 //@author wenzi1 
 //@date 20180604
 func Prepare(xmlbyte []byte) error {
-	patten := "<\\?xml\\s+.*?\\s+encoding=\"(.*?)\""
+	patten := "<\\?xml\\s+version\\s*=.*?\\s+encoding\\s*=\\s*[\\'|\"](.*?)[\\'|\"]\\s*\\?\\s*>"
 	charsetReader := func(charset string, input io.Reader) (io.Reader, error) {
 		reader, err := gcharset.GetCharset(charset)
 		if err != nil {