This reverts commit 4147ab73.

* add `end` to end of class definition
* add a blank line between explanation and example code

this commit removes some direct access to `env`.

This commit is to abstract the code away from the env hash.  It no
longer needs to have the routes key hard coded.

This changes the renderer class to store the controller and defaults as
an instance variable rather than allocating a new class.  You can create
a new renderer with an new env by calling `Renderer#new` or use new
defaults by calling `Renderer#with_defaults` and saving the return value
somewhere.

Also I want to keep the `env` private since I would like to change the
keys in the future.  This commit only translates particular keys that
the user requested.

this means the reader doesn't need to lock, but does have the added cost
of a new object created for every controller

The controller class is shared among threads, so we need to lock when
allocating the Renderer.

AC::Parameters does not inherit from HashWithIndifferentAccess
since #20868 by @sikachu

`Rack::Session::Abstract::ID` is now deprecated and
`Rack::Session::Abstract::Persisted` should be used instead.

In c546a2b0 this was changed to mimic how the browser behaves in a real
situation but left out types that were registered.

When this was changed it didn't take `text/plain` or `text/html` content
types into account. This is a problem if you're manipulating the
`Content-Type` headers in your controller tests, and expect a certain
result.

The reason I changed this to use `to_sym` is because if the
`Content-Type` is not registered then the symbol will not exist. If it's
one of the special types we handle that specifically (:json, :xml, or
:url_encoded_form). If it's any registered type we handle it by setting
the `path_parameters` and then the `request_parameters`. If the `to_sym`
returns nil an error will be thrown.

If the controller test sets a `Content-Type` on the request that `Content-Type`
should remain in the header and pass along the filename.

For example:
If a test sets a content type on a post
```
@request.headers['CONTENT_TYPE'] = 'text/plain'
post :create, params: { name: 'foo.txt' }
```

Then `foo.txt` should be in the `request_parameters` and params related
to the path should be in the `path_parameters` and the `Content-Type`
header should match the one set in the `@request`. When c546a2b0 was
committed `text/plain` and `text/html` types were throwing a "Unknown
Content-Type" error which is misleading and incorrect.

Note: this does not affect how this is handled in the browser, just how
the controller tests handle setting `Content-Type`.

This method is specifically about the content type so lets remove the
parameter.

create a singleton content type that just has nils, so that we don't
have to allocate a content type object all the time.

If someone sets just a charset, but depends on the implicit type from
rendering, this will store a strange content type header that looks like
this:  `; charset=blah`.  This is so that when the content type header
is parsed again, it will return nil for the actual type.

It turns out that the response object never really cares what the mime
type object is, so just use the string.

pull content-type setting to a private method to dry it up.

Instead of storing content type information in an ivar and a header,
lets move to just store the content type info in just the header.

we'll use this method later to lazily parse content type headers.

everything above metal really doesn't care about setting the content
type, so lets rearrange these methods to be in metal.

_set_content_type only does something when there is a request object,
otherwise the return value of _get_content_type is always ignored. This
commit moves everything to the module that has access to the request
object so we'll never to_s unless there is a reason

in the future I would like to make the header hash read only (or at
least remove guarantees that mutations will do anything).

It's only used there.

`CookieJar` is only at the start of the chain and has its own
request method, so we don't need it in the module.

It was the same in both legacy versions of the signed and encrypted cookie jars.

The `EncryptedCookieJar` already calls it for us, so just delegate to its `parse` implementation.

`SignedCookieJar`'s parse method already attempts to verify the message,
so we can just call super and try the old verifier if it fails.

Cuts down on the duplicated reading parts.

Gets rid of the option parsing and makes what the encryptor does stand out.

Lets us avoid worrying about parsing the options and doing just what we need.

Remove the clutter to make PermanentCookieJar's one change stand out.

Eventually this will be the superclass of all the chained jars.

SSL redirect:
* Move `:host` and `:port` options within `redirect: { … }`. Deprecate.
* Introduce `:status` and `:body` to customize the redirect response.
  The 301 permanent default makes it difficult to test the redirect and
  back out of it since browsers remember the 301. Test with a 302 or 307
  instead, then switch to 301 once you're confident that all is well.

HTTP Strict Transport Security (HSTS):
* Shorter max-age. Shorten the default max-age from 1 year to 180 days,
  the low end for https://www.ssllabs.com/ssltest/ grading and greater
  than the 18-week minimum to qualify for browser preload lists.
* Disabling HSTS. Setting `hsts: false` now sets `hsts: { expires: 0 }`
  instead of omitting the header. Omitting does nothing to disable HSTS
  since browsers hang on to your previous settings until they expire.
  Sending `{ hsts: { expires: 0 }}` flushes out old browser settings and
  actually disables HSTS:
    http://tools.ietf.org/html/rfc6797#section-6.1.1
* HSTS Preload. Introduce `preload: true` to set the `preload` flag,
  indicating that your site may be included in browser preload lists,
  including Chrome, Firefox, Safari, IE11, and Edge. Submit your site:
    https://hstspreload.appspot.com