Add the ability to save data to a stream.

- Useful when we don't want to save to a filename directly but stream
  it (this was something available in php-cloudfiles as well).
Add the ability to save data to a stream.

- Useful when we don't want to save to a filename directly but stream
  it (this was something available in php-cloudfiles as well).
Merge branch 'add-save-to-stream-to-objectstorage' of github.com:chmouel/php-opencloud into add-save-to-stream-to-objectstorage
Throw \Exceptions\ObjectError when SaveTostream.

If the resource is not a valid resource then throw
\Exceptions\ObjectError.
Merge pull request #121 from chmouel/add-save-to-stream-to-objectstorage

Add the ability to save data to a stream.