Update README.md

Fixes #2130.

Added FactoryGirl configuration details

Fix outdated method description in helper module

Fixes #2130.

link in Readme to source code of Paperclip::Processor

for better visibility and better User experience of documentation

Most contributors don't know to update the NEWS file when submitting
code.

Currently paperclip fails with `NoMethodError` on `nil` when file is not
present. Since `nil` is proper response from fog on missing files, and
this method already returns `false` if any error happen (see line 178),
returning `false` here would be properly handled on client code.

[closes #2173]

Update NEWS.

[ci skip]

Adds failing spec to command line dup check

[fixes #1670]
[fixes #2169]

[fixes #2164]

Bugfix: Dynamic fog directory

`Paperclip::Storage::Fog#host_name_for_directory` assumes a String-like
object is set and doesn't check if `@options[:fog_directory]` is
callable, while `Paperclip::Storage::Fog#directory` does. This extracts
a new method with the condition and refactors the other two methods to
call it.

Fixes #2018, #2093.

@melissawahnish noticed that while we are on beta v5 will not be found.

[ci skip]

This configuration constant was useful for supporting different versions
of AWS SDK. We don't any longer, and we can set the value directly.

[fixes #2148]

* `AWS::Core` is an AWS SDK v1 API, we can drop it
* We don't use the "I attach a" cucumber step

Brings back warning on not supported SDK versions.

Related: https://github.com/thoughtbot/paperclip/commit/25be0b25d67923e28419c6146e8f8307741a974b#commitcomment-16831800

We don't support AWS SDK v1 any longer.

Drops Rails 3 branches.

[fixes #2101]

Update example to add mime-types to file extensions

Remove Rails 3 snippets

Rails 3 is not supported anymore. We can safely remove mentions and
snippets for it.

Drop unused variable definition (`options`).

The old example gives deprecation warnings from recent 2.x versions of mime-types. As of f0bd25ad the Gemfile also allows version 3.0 or newer. The new example should work regardless of the version of the mime-types gem. [skip ci]

`>= 2.0.34` is the proper restriction. We weren't allowing `2.0.33`
before.

Paperclip 5 no longer supports aws-sdk v1. Having a lot of constraints
in one gem dependency caused issues when pushing the gem (ref:
https://github.com/rubygems/rubygems/issues/1564).

This commit simplifies the dependency restriction to `>= 2.0.33`.

Pairing with @kitop

Update NEWS.

[fixes #2134]
[ci skip]

Add Rails master appraisals in preparation for Rails 5

While working on this branch, Kito found that this test fails due to:

https://github.com/rails/rails/commit/6ec8ba16d85d5feaccb993c9756c1edcbbf0ba13#diff-fdcf8b65b5fb954372c6fe1ddf284c78R76

We are not yet sure if it's a bug in paperclip or in Rails itself. With
current `ActiveModel::Errors` implementation the following happens:

```
record.errors # => @messages = {}
record.errors.include?(:foo) # => false
record.errors # => @messages = { :foo => [] }
```

Which bit us in:
https://github.com/thoughtbot/paperclip/blob/69f18375333234b6f395300266e2612936bd242e/lib/paperclip/validators/attachment_file_name_validator.rb#L23

Another related Rails commit:
https://github.com/rails/rails/commit/b97035df64f5b2f912425c4a7fcb6e6bb3ddab8d

I worked around the issue by changing what we assert in this spec. I am
still not sure that this is a bug in current Rails master.

cc @kitop for review

Ref: https://github.com/rails/rails/commit/481e49c64f790e46f4aff3ed539ed227d2eb46cb

`silence_stream` was deprecated in Rails 4.2 and removed in Rails 5
because it was not thread safe. Paperclip is not running the tests in
threaded mode, it's safe to add the method back in a test support
module.

Ref: https://github.com/rails/rails/commit/2386daabe7f8c979b453010dc0de3e1f6bbf859d

Specifically:

> Chains of callbacks defined **with** a `:terminator` option will
> maintain their existing behavior of halting as soon as a `before_`
> callback matches the terminator's expectation. For instance,
> ActiveModel's callbacks will still halt the chain when a `before_`
> callback returns `false`.

In terminator callbacks, the `result` value changed to be a lambda now.
This change reflects that, updating the terminator to compare the result
of the block to `false`.

Also:

* Removes Rails 4.1 branch (we don't support it anymore)
* Rewrite for legibility: change `unless` for `if`

`bundle exec rails -v` was taking seconds every time, making the test
suite run very slow. This changes the code to compare the version
against `ActiveRecord::VERSION`, which is going to be the same one as
`rails -v`, making it much, much faster.

Simplifies condition: we no longer support Rails < 4.2, so we test for
`>= "5.0"` or fallback to `4.2` branch.

- Also bump Travis Ruby 2.2.x version to 2.2.4

We found that uploading large files to S3 would result in a socket error
("connection reset by peer") occasionally and lately much more
consistently. In researching this I saw that many people got this error
when uploading too large of a file without multipart chunking. I would
have assumed fog did this automatically but the default chunk size may
be too high. In order to address this I wanted to drop the chunk size to
100MB.

Rather than hard-code this I opted to expose a `fog_option`
configuration option that lets me pass any additional options I want to
the fog's `#create` call. This is similar to the `fog_attributes` option
implemented in CarrierWave which [addresses the same
problem](http://stackoverflow.com/a/11867978/201911).

We've been running this now for a week in production and it seems to
resolve the issue.

https://github.com/thoughtbot/paperclip/pull/2135

Related with https://github.com/thoughtbot/paperclip/issues/2122

[ci skip]

See https://www.ruby-lang.org/en/news/2016/02/24/support-plan-of-ruby-2-0-0-and-2-1/

Remove attr_protected related specs (was removed in rails 4)