Documented devkit requirement for Windows

* Change `rbx` to `rbx-2`
* Mark `rbx-2` as allow-failure again

Fixes #1550

Remove typo in contributing guidelines

- With fixes as suggested by mike-burns

Remove extraneous 'not'.

https://github.com/thoughtbot/paperclip/issues/1543

added :preserve_files notes to the README

Document requirement for file command.

Update Capistrano Task example for working in 3.x version

Optionally disable inspecting EXIF for orientation

Ensure required validations accepts subclasses

Add german locale file

Locale file for spanish

* Extract private methods
* Remove trailing conditionals
* Remove explicit returns
* Remove `.self`

Add docs badge to README

There's nothing they can be spoofing, and there's little danger of a
webserver accidentally sending a dangerous Content-Type with a file that
has no extension. If the browser chooses to interpret it in a dangerous
manner, no server-side library on earth can change that.

This isn't specifically related to RSpec, but is built off the branch
and is part of an effort to get the CI build green.

First off, sqlite3 needs to be exactly v1.3.8.
Need to make sure both racc and rubysl are in the Gemfiles.
RBX's File.join doesn't like nil at all.
RBX also doesn't like to remove a constant that doesn't exist yet.