fix lists with paragraph content

Another super hack, though hopefully the PR gives you the gist of the problem. List items that are separated by a blank line end up having a list marker on a separate line from the content...which breaks the list in AsciiDoc. I've done a quick hack here to not put a blank line before start of a paragraph when inside a list.

In general, I think the serializer should not put a blank link at the top of content, only at the bottom of content. That way, you can control better where endlines get placed. When they are added above and below, you lose a lot of control when using the recursive decent visitor strategy.