How to treat single line breaks as <br> in showdown?

How to have GitHub style treating of newlines using showdown?

I have tried an extension that does something like:

return text.replace(/[ ]*\n/g, "<br />\n")

It works in some cases but breaks lists for example.

Okay so I came up with extension which does that.

/**
 * Showdown extension for GFM newlines.
 * 
 * In very clear cases, let newlines become <br/> tags.
 *
 * This implementation is adopted from showdown-ghost.
 *
 */
(function () {
    var newline = function () {
        return [{
            type: 'lang',
            filter: function(text) {
                return text.replace(/^( *(\d+\.  {1,4}|[\w\<\'\">\-*+])[^\n]*)\n{1}(?!\n| *\d+\. {1,4}| *[-*+] +|#|$)/gm, function(e) {
                    return e.trim() + "  \n";
                })
            }
        }];
    };

    if (window.showdown) {
        window.showdown.extensions.newline = newline;
    }
})();

This is working great for me, although the regex is not 100% tested and will probably fail in some rare cases, so consider yourself warned.