add fs.statSync and rudimentary fs.Stat support (just the is* methods)
make sure we wrap the intrinsic in an expression-statement so escodegen doesn't puke
make sure filename is stored in @filename
add a terribly naive path.join
allow imports to specify directories as well as js files.

when importing, check if the $source is a directory.  if it is, attempt to load $source/index.js.
Otherwise fallback to loading $source.js