Use async function for bin

The better to handle win32's EBUSY.

Fix #74

bin.js

@@ -18,16 +18,23 @@ var args = process.argv.slice(2).filter(function(arg) {
 if (help || args.length === 0) {
   // If they didn't ask for help, then this is not a "success"
   var log = help ? console.log : console.error
-  log('Usage: rimraf <path>')
+  log('Usage: rimraf <path> [<path> ...]')
   log('')
   log('  Deletes all files and folders at "path" recursively.')
   log('')
   log('Options:')
   log('')
   log('  -h, --help    Display this usage info')
   process.exit(help ? 0 : 1)
-} else {
-  args.forEach(function(arg) {
-    rimraf.sync(arg)
+} else
+  go(0)
+
+function go (n) {
+  if (n >= args.length)
+    return
+  rimraf(args[n], function (er) {
+    if (er)
+      throw er
+    go(n+1)
   })
 }