LIs with trailing whitespace
br should be replaced with two spaces and newline

Otherwise, it will be rendered without line break once converted back to html
br should be replaced with two spaces and newline

Updated tests
Merge pull request #53 from rasmusvhansen/patch-1

PR: br should be replaced with two spaces and newline
Merge pull request #51 from stevenweber/li-spacing

LIs with trailing whitespace
added executable