Moved configuration to assocative array and implemented header/footer support.

I moved the configuration options to an associative array as per #5 to prevent argument hell when we support more options in the future.

I also implemented header and footer support. To use, just include 2 JS variables (`h2pHeader` and `h2pFooter`) in your html document/string:

```javascript
<script type="text/javascript">

	var h2pHeader: {
		height: "1cm",
		contents: function(pageNum, numPages) { return pageNum + "/" + numPages; }
	};

	var h2pFooter: {
		height: "1cm",
		contents: function(pageNum, numPages) { return pageNum + "/" + numPages; }
	}
 };
</script>
```