feat(favicon): add plugin to expose favicon from icon.png (#1942)

* feat(favicon): add plugin to expose favicon from icon.png

* chore(favicon): clean up formatting and remove unnecessary line breaks

quartz/plugins/emitters/index.ts

@@ -5,6 +5,7 @@ export { ContentIndex as ContentIndex } from "./contentIndex"
 export { AliasRedirects } from "./aliases"
 export { Assets } from "./assets"
 export { Static } from "./static"
+export { Favicon } from "./favicon"
 export { ComponentResources } from "./componentResources"
 export { NotFoundPage } from "./404"
 export { CNAME } from "./cname"