Embeds a critical CSS file into a page's HTML head, and loads the rest of non-critical CSS asynchronously. INTRODUCTION This module looks for a css file inside your theme directory. This css filename should match any of: bundle type (i.e., "article.css") entity id (i.e., "123.css") url (i.e., "my-article.css") If none of the previous filenames can be found, this module will search for a file named "default-critical.css". A hook is provided ("critical_css_file_paths_suggestion") in case another filename is needed.