Support python3

It was confirmed that it works on python 2.7 and 3.3.
My environment is Ubuntu 13.04.
Simply escape sequence
Create formatting function that can preserve the order

source json: {"b":1,"a":2}

json-beautify:
{
    "a": 2,
    "b": 1
}

ordered-json-beautify:
{
    "b": 1,
    "a": 2
}