Expose main constructor, fallback on document

This is a similar behavior to jQuery.
Behave as an array

This adds the jQuery-like UI where the Helix object will look and behave
like a regular Array. So `$('div')` would actually return
`[<HTMLElement>, ...]`, yet still expose regular Helix functions.
Allow passing of DOM elements or list of DOM elements to constructor

This is also per jQuery behavior.
Add find function
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