Add an active attachment to attach the active link behavior anywhere #96
Description
Motivation
Since Sveltekit is a possiblity now and it works with regular HTML anchor elements, and because at least the Bulma styling library applies the active styling to the <li> element and not the anchor element, it is desirable to encapsulate this feature as an attachment that can be used on any element or component.
Current Hold-up
To complete this task, we need sveltejs/svelte#16873 resolved to be able to fully support the ClassValue data type currently used to type ActiveState.class.