Support named slots #103
Description
Currently ReactiveElements supports the default slot
<example-component>
<div>this content goes in the default slot</div>
</example-component>The web components spec supports multiple named slots.
https://developer.mozilla.org/en-US/docs/Web/Web_Components/Using_templates_and_slots#Adding_flexibility_with_slots
<example-component>
<div>this content goes in the default slot</div>
<span slot="my-text">Let's have some different text!</span>
</example-component>