@byContent should have a default functionality when no parameters are passed

Like the @byAttrVal annotation, when no parameters are passed, there is a default behaviour (in that case, matching the attribute with the same name of the property).

When I use @byContent without parameters, `@byContent()`, I expect a list of nodes, or a node (like a React.Fragment) wrapping everything inside the web component, maybe like the normal `this.props.children` property.