No unicode support about notedown HOT 2 CLOSED

> notedown test.md
{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "test.md\n",
    "®åéøß"
   ]
  }
 ],
 "metadata": {},
 "nbformat": 4,
 "nbformat_minor": 0
}

Traceback (most recent call last):
  File "/Users/scott/anaconda/bin/notedown", line 11, in <module>
    sys.exit(cli())
  File "/Users/scott/anaconda/lib/python2.7/site-packages/notedown/main.py", line 261, in cli
    writer.write(notebook, op)
  File "/Users/scott/anaconda/lib/python2.7/site-packages/IPython/nbformat/__init__.py", line 161, in write
    fp.write(s)
UnicodeEncodeError: 'ascii' codec can't encode characters in position 85-89: ordinal not in range(128)