Make shift-backspace do the same as backspace in editors

This can be useful when typing an all-caps word; if you mistype one
letter, you can delete it without having to let go of shift.

pkg/gocui/edit.go

@@ -41,6 +41,7 @@ func SimpleEditor(v *View, key Key) bool {
 		key.Equals(NewKeyStrMod("d", ModAlt)):
 		v.TextArea.ForwardDeleteWord()
 	case key.Equals(NewKeyName(KeyBackspace)),
+		key.Equals(NewKey(KeyBackspace, "", ModShift)),
 		key.Equals(NewKeyStrMod("h", ModCtrl)):
 		v.TextArea.BackSpaceChar()
 	case key.Equals(NewKeyStrMod("d", ModCtrl)),