ignore struct field if form tag value is '-'

@@ -195,6 +195,8 @@ func ParseForm(form url.Values, obj interface{}) error {
 		var tag string
 		if len(tags) == 0 || len(tags[0]) == 0 {
 			tag = fieldT.Name
+		} else if tags[0] == "-" {
+			continue
 		} else {
 			tag = tags[0]
 		}

@@ -104,8 +104,8 @@ func TestInSlice(t *testing.T) {
 
 func TestParseForm(t *testing.T) {
 	type user struct {
-		Id    int
-		tag   string      `form:tag`
+		Id    int         `form:"-"`
+		tag   string      `form:"tag"`
 		Name  interface{} `form:"username"`
 		Age   int         `form:"age,text"`
 		Email string
@@ -114,6 +114,8 @@ func TestParseForm(t *testing.T) {
 
 	u := user{}
 	form := url.Values{
+		"Id":       []string{"1"},
+		"-":        []string{"1"},
 		"tag":      []string{"no"},
 		"username": []string{"test"},
 		"age":      []string{"40"},