Option to preserve whitespace from markdown

When editing notes I often find myself looking more at the markdown than the formatted output. It's just so easy to format things with a monospace font and the tab key. To get the same thing in the formatted output I need to put in a lot of extra tags.

It would be nice to have a markdown option that preserves whitespace. Replace all instances of more than one space with   in the output, and tabs with 4x  .

Also newlines would generate one <br/> for each, i.e. not collapse multiple newlines into one.