Don't include linebreaks in whitespace
Raw URLs can't end with a . or a ,
Don't intersperse inline chunks with spaces
Fix tests
Break out of lists properly upon exiting a block.
Don't allow square brackets in raw URLs
Allow lists to have child lists of any type

eg, the following is now valid:

** World

And renders as

<ol>
<li>Hello
<ul><li>World
</li></ul></li></ol>