* Auto-link for documents. If there is an `org` directive in the first doc
block of the file then it is used as the file link definition. If there is no
such `org` directive then on is created automatically. This resolves issue
#0008. There is a new LinkAnchor type for these links: `LinkType.FileLink`
* Multiple `org` directives per DocBlock are now allowed. There is a new
LinkAnchor link type for these link: `LinkType.InlineLink`.
* Refactored `LinkType.OrgLink` to be `LinkType.BlockLink`.
* Tweaked CSS
* Refactored `LiterateMarkdownGenerator.emit(DocBlock)` for simplicity.
