Added smart_list support for *

Numbered lists, `+` and `-` all work properly.

Unfortunately, `*` does not.  

Looks like the regexes from https://github.com/demon386/SmartMarkdown/pull/5 are just a little off:
https://github.com/mhenry07/SmartMarkdown/commit/6f229aa8bc204680e8fee775e3515fd416039a4a