Python: missing explicit dependency on "six" package
Platform: OSX 10.9, pip: 1.5.5, js-beautify: 1.5.1

It appears that "six" is not explicitly listed as a dependency in setup.py.

```
$ sudo pip install jsbeautifier
Downloading/unpacking jsbeautifier
  Downloading jsbeautifier-1.5.1.tar.gz
  Running setup.py (path:/private/tmp/pip_build_root/jsbeautifier/setup.py) egg_info for package jsbeautifier
    Traceback (most recent call last):
      File "<string>", line 17, in <module>
      File "/private/tmp/pip_build_root/jsbeautifier/setup.py", line 4, in <module>
        from jsbeautifier.__version__ import __version__
      File "jsbeautifier/__init__.py", line 8, in <module>
        import six
    ImportError: No module named six
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):

  File "<string>", line 17, in <module>

  File "/private/tmp/pip_build_root/jsbeautifier/setup.py", line 4, in <module>

    from jsbeautifier.__version__ import __version__

  File "jsbeautifier/__init__.py", line 8, in <module>

    import six
```

Temporary workaround:

```
pip install six
```

diff --git a/python/setup.py b/python/setup.py
index e7d85838..6e539a5c 100755
--- a/python/setup.py
+++ b/python/setup.py
@@ -14,5 +14,6 @@ setup(name='jsbeautifier',
       scripts=['js-beautify'],
       packages=['jsbeautifier', 'jsbeautifier.tests',
                 'jsbeautifier.unpackers', 'jsbeautifier.unpackers.tests'],
+      install_requires=["six>=1.6.1"],
       license='MIT',
      )
['python/setup.py']