Comments html5

I modeled the new comments markup after the default html5 comments template in core. #60 

Before merging, I'd like feedback on one thing. /cc @emhr @scottnix

The comment author, permalink etc gets wrapped in a `<footer>` element with class `comment-meta`. I then changed the class of the former `comment-meta` div to `comment-metadata`, and the same for the corresponding output filter. I am inclined to also change the name of the function to match, but wonder if the name changing will be a source of confusion and/or breakage.

Current comment markup:

```html
<li id="comment-{id}" >
	<article id="comment-body-{id}" class="comment-body">
		<footer class="comment-meta">
			<div class="comment-author vcard"> {thematic_commenter_link}</div><!-- .comment-author -->
			
			<div class="comment-metadata">';
				<time datetime="'. get_comment_time( 'c' ). '">{comment_posted_at}</time>';
				{comment permalink}
				{comment edit link}
			</div>
			
			{comment moderation notice}

		</footer><!-- .comment-meta -->
		
		<div class="comment-content">
			{comment_text}
		</div><!-- .comment-content -->
		{comment reply link}
	</article><!-- .comment-body -->
```

The function outputting the `.comment-metadata` div is called `thematic_commentmeta()`. This is the one I'm considering renaming to `thematic_commentmetadata()`, just for consistency. Or should we keep the `comment-meta` class on the div and give the footer element another class name?