Add formxxx attributes (for <input type="submit"> element) (#241)

Hello,

A small patch to add the following attributes:

- formaction
- formenctype
- formmethod
- formnovalidate
- formtarget

These attributes are useful in `<input type="submit">` element: [MDN
documentation](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/submit#additional_attributes)

1 files changed, 5 insertions, 0 deletions

diff --git a/html/attributes_test.go b/html/attributes_test.go
index cfb64b5..9b668b2 100644
--- a/html/attributes_test.go
+++ b/html/attributes_test.go
@@ -21,6 +21,7 @@ func TestBooleanAttributes(t *testing.T) {
 		{Name: "controls", Func: Controls},
 		{Name: "defer", Func: Defer},
 		{Name: "disabled", Func: Disabled},
+		{Name: "formnovalidate", Func: FormNoValidate},
 		{Name: "loop", Func: Loop},
 		{Name: "multiple", Func: Multiple},
 		{Name: "muted", Func: Muted},
@@ -61,6 +62,10 @@ func TestSimpleAttributes(t *testing.T) {
 		{Name: "dir", Func: Dir},
 		{Name: "for", Func: For},
 		{Name: "form", Func: FormAttr},
+		{Name: "formaction", Func: FormAction},
+		{Name: "formenctype", Func: FormEncType},
+		{Name: "formmethod", Func: FormMethod},
+		{Name: "formtarget", Func: FormTarget},
 		{Name: "height", Func: Height},
 		{Name: "hidden", Func: Hidden},
 		{Name: "href", Func: Href},