fix(extractor): Workaround some encoding errors.

Use BeautifulSoup's UnicodeDammit to convert retrieved HTML.
That fixes some errors like:
- UnicodeDecodeError: 'utf8' codec can't decode byte 0xab in position 75: invalid start byte
- ValueError: All strings must be XML compatible: Unicode or ASCII, no NULL bytes or control characters
Example with error http://www.teenvogue.com/fashion/2014-10/chanel-party.
Merge pull request #50 from cronycle/fix/encoding-errors

fix(extractor): Workaround some encoding errors.