Serve the CSS in a way that doesn't damage performance

[Photosynthesis]

This plugin is great, but unusable on sites where performance is a concern until the CSS is delivered in a way that doesn't bypass caching. In its current form it bypasses the cache (because of the query string in the stylesheet URL), and the whole Wordpress environment has to be loaded in order to return the CSS (because it's being output by plugin PHP code). This combination makes it very problematic for performance.

This could be fixed by writing the CSS out to an actual file. A possibly simpler solution would be to use a WP API endpoint to serve the CSS from a cachable URL without a query string. This would still require PHP and Wordpress to generate the CSS the first time, but at least it could be cached.

Thanks for building a nice simple plugin!