Improve Fog Loading

[plribeiro3000]

This PR is an attempt to create an easy support for both providers within fog and the ones that were already extracted.
Instead of rely on constant definition to load fog support, now it depends on a configuration.
If fog_provider is not defined carrierwave will try to load fog completely. If the user has only fog-aws on its Gemfile it will fail.
The use won't need to require any fog specifics before carrierwave anymore because carrierwave will do that now.
The optimized loading of fog is not necessary if the user is using an extracted provider and google was extracted so i did some changes on README reflecting this.

Let me know if i need to change something else or something is wrong.

[bensie]

Awesome, thanks!

[plribeiro3000]

Wow. Thank you for the fast support. ❤️

[plribeiro3000]

@bensie When will be a new release including this changes?

[avgerin0s]

@plribeiro3000 Nice! :) Thanks

[plribeiro3000]

@bensie @eavgerinos Did i forgot something in here?
In a second thought i think the tests should break somehow. Or perhaps i should add tests for this new config. Do you guys think it would be good to have tests for this?

[thejbsmith]

I was having the same issue, and this fixed it for the most part.

One note: config.fog_provider = 'fog-aws' should be config.fog_provider = 'fog/aws'. With the directory structure of the fog-aws gem, there is no fog-aws.rb file, the file is located at fog/aws.rb.

Once I got that switched, this seems to work great for me. Probably worth updating the README.

[avgerin0s]

@thejbsmith Fixed :)