Added new listing syntax

listing syntax:
```
~~TODOLIST~~
~~TODOLIST completed:yes~~
~~TODOLIST completed:no assigned:no~~
~~TODOLIST assigned:yes~~
~~TODOLIST assigned:@User~~
~~TODOLIST assigned:@User,@work~~
~~TODOLIST assigned:User,work,@user2~~
```

==searchpattern==
The searchpattern listing is broken by moving `syntax.php` to
`syntax/todo.php`. It can be fixed by let searchpattern allow _ of the
`todo_todo` and removing the plugin_is_disabled checks. These last
checks require as input the plugin name `todo` instead of plugin
component name `todo_todo`