Remove wrong content-encoding handling

Content-Encoding header is not to specify character encodings, but
specify content compressing (encoding).
http://msdn.microsoft.com/ja-jp/library/windows/desktop/aa383955(v=vs.85).aspx
Allow IO as body

For example BlobService#create_block_blob says its content is
IO or String but actually doesn't.
Merge branch 'allow-body-as-io'
Merge branch 'content-encoding-is-not-character-encoding'