Add support for classes on li-tags using <>

"*<foo> Lorem Ipsum" will now generate "<li class="foo">Lorem Ipsum</li>". It works for both ul and ol but ol is a bit crude and the class goes after the dot, e.g. "1.<foo>" but changing would require a larger rewrite of the RE and logic.
Add options for li-class.

Defaulting to disabled to maintain better compability, but it still parses and swallows the <> block. If a user had previously entered "*<..> " it would show up literal but now it will be a list.
Improving attribute serialization for li-class.
Merge pull request #1 from NitroXy/li_class

Add support for classes on li-tags using <>