markdown: add test for multiple lists

I was just going to suggest adding an additional test to ensure that the code handles multiple lists properly. In my solution to the problem, I used a regex to insert the `

` tags at the appropriate locations. Originally I had just `(
• .*
)` which passed all the tests, but which will work ONLY WHEN YOU HAVE A SINGLE LIST in your markdown text. If you have more than one, it'll put a single pair of `
` tags around all of them (beginning of the first, end of the last) and whatever headers and paragraphs are found between.

My current regex `(

• .*?
)(<[ph])|(
• .*
)` handles multiple lists correctly, as far as I can tell. The first half (before the '|') catches string-initial or internal lists, while the latter half will kick in to handle string-terminal lists.