Adds author to front matter

This will likely need some configuration to enable it, I threw this
together at work but if there is intrest I can add that.

src/parser.js

@@ -110,6 +110,10 @@ function getPostCoverImageId(postData) {
 	return id;
 }
 
+function getAuthor(post) {
+	return post.creator[0]
+}
+
 function collectAttachedImages(channelData) {
 	const images = getItemsOfType(channelData, 'attachment')
 		// filter to certain image file types