Fix UnicodeDecodeError while file uploading

This bug appears when method is unicode and request got files
argument, e.g.:

    >>> requests.request(u'post', u'http://httpbin.org/post',
    ...                  files={u'file': open('README.rst', 'rb')})
    UnicodeDecodeError: 'ascii' codec can't decode byte 0xc5 ...
Bump version and update HISTORY
Merge pull request #51 from uploadcare/version-1.0.2

Fix UnicodeDecodeError