When testing:

```ruby
post articles_path, params: { article: { title: 'Ahoy!' } }, as: :json
```

It's common to want to make assertions on the response body. Perhaps the
server responded with JSON, so you write `JSON.parse(response.body)`.
But that gets tedious real quick.

Instead add `parsed_body` which will automatically parse the reponse
body as what the last request was encoded `as`.

Add `as` to encode a request as a specific mime type.

Fix edge case with ActionView::Template::Error reraise

set association name to generated fixtures if attribute is reference

Fix tiny grammar.

Fix typo

Fix grammar errors in security and migrations docs master [ci skip]

Fixed errors in rails migrations docs [ci skip]

Fixed errors in rails security docs [ci skip]

We don't need to use active support in this case because we know the
type that will be returned.

Update documentation regarding initializers

- Remove ActionController `logger` and `initialize_framework_caches`
  which were merged into `set_configs` in fbc9d0f4
- Rename ActiveRecord `set_reloader_hooks` changed in 283a0876
- Add missing initializers for ActionController and ActiveRecord

remove description of `render :nothing` from guide [ci skip]

`:nothing` option was deprecated in 44781b6e

Fix typo [ci skip]

For better or worse, anonymous `*` args will allocate arrays.  Ideally,
the interpreter would optimize away this allocation.  However, given the
number of times we call `html_safe` it seems worth the shedding idealism
and going for performance.  This line was the top allocation spot for a
scaffold (and presumably worse on real applications).

```
[aaron@TC rails (master)]$ cat xor.rb
a = "\x14b\"\xB4P8\x05\x8D\xC74\xC3\xEC}\xFDf\x8E!h\xCF^\xBF\xA5%\xC6\xF0\xA9\xF9x\x04\xFA\xF1\x82"
b = "O.\xF7\x01\xA9D\xA3\xE1D\x7FU\x85\xFC\x8Ak\e\x04\x8A\x97\x91\xD01\x02\xA4G\x1EIf:Y\x0F@"

def xor_byte_strings(s1, s2)
  s1.bytes.zip(s2.bytes).map { |(c1,c2)| c1 ^ c2 }.pack('c*')
end

def xor_byte_strings2(s1, s2)
  s2_bytes = s2.bytes
  s1.bytes.map.with_index { |c1, i| c1 ^ s2_bytes[i] }.pack('c*')
end

require 'benchmark/ips'
require 'allocation_tracer'

Benchmark.ips do |x|
  x.report 'xor_byte_strings' do
    xor_byte_strings a, b
  end

  x.report 'xor_byte_strings2' do
    xor_byte_strings2 a, b
  end
end

ObjectSpace::AllocationTracer.setup(%i{type})
result = ObjectSpace::AllocationTracer.trace do
  xor_byte_strings a, b
end
p :xor_byte_strings => result
ObjectSpace::AllocationTracer.clear
result = ObjectSpace::AllocationTracer.trace do
  xor_byte_strings2 a, b
end
p :xor_byte_strings2 => result
[aaron@TC rails (master)]$ ruby -I~/git/allocation_tracer/lib xor.rb
Calculating -------------------------------------
    xor_byte_strings    10.087k i/100ms
   xor_byte_strings2    11.339k i/100ms
-------------------------------------------------
    xor_byte_strings    108.386k (± 5.8%) i/s -    544.698k
   xor_byte_strings2    122.239k (± 3.0%) i/s -    612.306k
{:xor_byte_strings=>{[:T_ARRAY]=>[38, 0, 0, 0, 0, 0], [:T_STRING]=>[2, 0, 0, 0, 0, 0]}}
{:xor_byte_strings2=>{[:T_ARRAY]=>[3, 0, 0, 0, 0, 0], [:T_DATA]=>[1, 0, 0, 0, 0, 0], [:T_IMEMO]=>[2, 0, 0, 0, 0, 0], [:T_STRING]=>[2, 0, 0, 0, 0, 0]}}
```

[ci skip] Fix grammar

fix 'method redefined' warnings

Fix a typo

Replace `a` with `an`

This reverts commit 8c3cca5e, reversing
changes made to 9dcf67c4.

Reason: https://github.com/rails/rails/pull/23562#issuecomment-181442569

Update rails-html-sanitizer version to  v1.0.3

rails-html-sanitizer 1.0.2 is vulnerable: https://groups.google.com/d/msg/rubyonrails-security/uh--W4TDwmI/m_CVZtdbFQAJ

Remove references to Rails 4 from assets guide [ci skip]

revert dev:cache to rake task, fixes #23410

Add numeric type in the doc [ci skip]

Follow up to #23508.

remove `faye-websocket` dependency from README [ci skip]

`faye-websocket` gem is no longer used from 322dca29.

config examples for ActionCable now use Rails.application.config.action_cable