Fix list grouping in test/markdown.md

marked appears to require a trailing newline to correctly format list blocks. See chjj/marked#358 for a potential fix.
Created test for indented list starting with a checkbox.
Fix list bulleting position

on lists where the first item has a checkbox.
Merge pull request #3 from OnAzureWings/bug/greedy-label-wrapping

Fix greedy checkbox/label wrapping on list elements