It is possible for a UnicodeEncodeError to occur when stripping the namespace

```
File "/home/policystat/env/lib/python2.6/site-packages/pydocx/DocxParser.py", line 108, in __init__
    self._build_data(path, *args, **kwargs)
  File "/home/policystat/env/lib/python2.6/site-packages/pydocx/DocxParser.py", line 72, in _build_data
    self.root = parse_xml_from_string(self.document_text)
  File "/home/policystat/env/lib/python2.6/site-packages/pydocx/utils.py", line 420, in parse_xml_from_string
    return cElementTree.fromstring(remove_namespaces(xml))
  File "/home/policystat/env/lib/python2.6/site-packages/pydocx/utils.py", line 78, in remove_namespaces
    return cElementTree.tostring(root)
  File "/usr/lib/python2.6/xml/etree/ElementTree.py", line 1009, in tostring
    ElementTree(element).write(file, encoding)
  File "/usr/lib/python2.6/xml/etree/ElementTree.py", line 663, in write
    self._write(file, self._root, encoding, {})
  File "/usr/lib/python2.6/xml/etree/ElementTree.py", line 707, in _write
    self._write(file, n, encoding, namespaces)
  File "/usr/lib/python2.6/xml/etree/ElementTree.py", line 707, in _write
    self._write(file, n, encoding, namespaces)
  File "/usr/lib/python2.6/xml/etree/ElementTree.py", line 707, in _write
    self._write(file, n, encoding, namespaces)
  File "/usr/lib/python2.6/xml/etree/ElementTree.py", line 707, in _write
    self._write(file, n, encoding, namespaces)
  File "/usr/lib/python2.6/xml/etree/ElementTree.py", line 705, in _write
    file.write(_escape_cdata(node.text, encoding))
  File "/usr/lib/python2.6/xml/etree/ElementTree.py", line 807, in _escape_cdata
    return _encode_entity(text)
  File "/usr/lib/python2.6/xml/etree/ElementTree.py", line 792, in _encode_entity
    return _encode(pattern.sub(escape_entities, text), "ascii")
  File "/usr/lib/python2.6/xml/etree/ElementTree.py", line 751, in _encode
    return s.encode(encoding)
UnicodeEncodeError: 'ascii' codec can't encode character u'\U0010001f' in position 0: ordinal not in range(128)
```

Figure out the encoding of the document and pass that into `tostring`