This PR allows you to assign a URI object to an attachment. The
attachment is downloaded and saved with a proper content type and
filename based on the path of the URL.

* Fixed tests and functionality for new fog and removed the fixed version from the gemspec
* Set time to 3600 from the current time so expiring actually works

* Added test for checking if path gets interpolated correctly without passing
  :path or :url options
* gsub default :rails_root filesystem-like path to nothing for Fog storage,
  just like in S3 Storage.

`s3_protocol` now returns the protocol without a colon. If you need a
colon, you can pass in `true` as a second argument.

This might not be a best solution, so any better patch that does not
introduce a regression is welcome.

Fixes #921

* Add StyleTokenNotFound in Errors
* Adjust tests to make sure :style present where not currently defined

Fixes #902

Fixes #883

Re-fix of #838, #766, #911

IMPORTANT: There is a bug in the current release of Fog (1.3.1) that will
return a broken expiring URL when the bucket name is valid for a subdomain.
This is fixed per https://github.com/fog/fog/pull/857 but not released
in the gem yet. I have added currently FAILING tests for these cases that
should pass when a new Fog is released.

This relates to #817