Expose refractor alias function on prism light syntax highlighter

This allows client applications to register aliases for languages without having to try and access refractor directly. Useful for aliasing languages under other acronyms.

src/prism-light.js

@@ -5,4 +5,7 @@ const SyntaxHighlighter = highlight(refractor, {});
 SyntaxHighlighter.registerLanguage = (_, language) =>
   refractor.register(language);
 
+SyntaxHighlighter.alias = (name, aliases) =>
+  refractor.alias(name, aliases);
+
 export default SyntaxHighlighter;