replace Paperclip::Attachment#initialize options with an AttachmentOptions instance

Introducing `:restricted_characters` in Paperclip::Attachment.default_options  so people can override their blacklist characters by override that setting.

Fixes #703

Simple addition to allow procs in the fog_config_options (bucket-name, authentication, and host)

Travis CI deprecated and remove the rbx-2.0 alias after rbx project
merged stuff back to master branch.

Closes #678. Closes #450.

If a model has an existing attachment and styles, and later a new attachment is added (not just new styles), "rake paperclip:refresh:missing_styles" would crash with "TypeError: can't convert nil into Array".

#fingerprint now consistently returns nil before and after saving an attachment if the value can't be written to the db.

Add documentation for including `aws-sdk` in Gemfile