Officially deprecate using JavaScript API for inserting icons into predefined places

It is a requirement to every modern website to work without JavaScript enabled. Modern unfit web developres often use garbage like Bootstrap's JS part recklessly, resulting in the websites completely unusable without JavaScript, even if the same effect is achieved without any bit of JavaScript [in pure CSS+HTML](https://github.com/you-dont-need/You-Dont-Need-Javascript). Some developers intentionally do that because of their website is full of tracking and advertising scripts making them profit. Unfit web developres usually just don't care and are driven by fashion. `feather.replace` encourages reliance on JavaScript.

I advise to officially deprecate using of `feather.replace` and other JS API for inserting icons into predefined places and advise using HTML markup for that in production.

Start by reviewing the `feather.replace` API and the current project guidance for inserting icons. Determine what officially deprecating this API would require and how HTML markup should be recommended instead; done would mean the project’s public guidance and any relevant API deprecation treatment clearly reflect that decision.

Written by the indexing model from the issue text.