This is very rough, and at the moment only goes as far as satisfying my own needs.
It converts from markdown to xmarkdown.
npm install md2xmd
From command line:
$ md2xmd foo.md > foo.xmd
Or with code:
var md2xmd = require("md2xmd");
var src = fs.readFileSync("foo.md","utf8");
console.log(md2xmd(src));