[ci skip] Adding a note to Action Mailer Basics documentation that Google increased its security measures

security measures so using the example for Gmail will return a “Password Incorrect” error,
and you will receive an email from Google that they blocked a sign-in attempt.  You can change
your Gmail settings or use another ESP.

I discovered this when I was testing a simple mailer example app and was just going to
use my personal Gmail account for the test.  I think it would be best to note this change
since now Gmail may not be the best option for a quick test.  I hope this saves time for other Rails
developers.  The Gmail example does show a good example of how to configure the smpt settings.

replace each with each_key when only the key is needed

Using each_key is faster and more intention revealing.

Calculating -------------------------------------
                each    31.378k i/100ms
            each_key    33.790k i/100ms
-------------------------------------------------
                each    450.225k (± 7.0%) i/s -      2.259M
            each_key    494.459k (± 6.3%) i/s -      2.467M

Comparison:
            each_key:   494459.4 i/s
                each:   450225.1 i/s - 1.10x slower

The tests and methods were hard to read with `options[:options]` all
over the place. This refactoring makes the code easier to understand.

The change came out of work for moving the underlying code of controller
tests to integraiton tests.

Allow a custom dispatcher to be provided to routing.

Using the string version of the class reference is now deprecated when
referencing middleware. This should be written as a class not as a string.

Deprecation warning that this change fixes:
```
DEPRECATION WARNING: Passing strings or symbols to the middleware
builder is deprecated, please change
them to actual class references.  For example:
  "ActionDispatch::ShowExceptions" => ActionDispatch::ShowExceptions
```

`extra_keys` is a confusing variable name because it's not clear what is
"extra". This renames it to `query_string_keys` so it's clear that the
"extra" is just the query string.

We were doing extra work that could be pushed off to Integration test
and SharedRoutes. Creating an extra module isn't necessary when those
are created by their respective classes.

use uuid method to define the UUID type [ci skip]

[ci skip] Add an explanation for `status` option

scope so that they are available to subclasses.

people should be accessing request information through the request
object, not via the env hash.  If they really really want at the env
hash, then they can get it off the request.

remove the setter.  The request object manages the env hash, so any
mutations need to go through it

Looks like this was left over from converting Rails to Rack.  I think
it's safe to remove now.

Actions are processed through `dispatch`, so they should have the
request set on them before any user land code can be executed.  Lets
stop setting _env on the controller, and give access to it through the
`env` method.

since we only work with instances of classes, it greatly simplifies the
`Middleware` implementation.

Convert things like this:

  middleware.use "Foo::Bar"

to this:

  middleware.use Foo::Bar

use a strategy pattern to calculate the conditional in `valid?` in
advance.

We should do the hard work outside the constructor.  Also fix the tests
to not directly construct middleware objects, but to go through the
stack object.

Proc.new will pick up the passed in block, but since it's a default
param, it won't get evaluated unless someone doesn't pass in an app.  It
will raise an exception if no block is provided.

Remove XML Serialization from core

Discussion https://github.com/JuanitoFatas/fast-ruby/pull/59#issuecomment-128513763

This includes the following classes:

- ActiveModel::Serializers::Xml
- ActiveRecord::Serialization::XmlSerializer

this is another place that we should stop directly accessing the env
hash and let the request object take care of that for us

in_batches using ids

Fix doc typo

Prevent the default block for mattr_accessor being called multiple times

Only invoke the default block for mattr_accessor once so that it does not cause issues if it is not idempotent

`in_batches` yields Relation objects if a block is given, otherwise it
returns an instance of `BatchEnumerator`. The existing `find_each` and
`find_in_batches` methods work with batches of records. The new API
allows working with relation batches as well.

Examples:

    Person.in_batches.each_record(&:party_all_night!)
    Person.in_batches.update_all(awesome: true)
    Person.in_batches.delete_all
    Person.in_batches.map do |relation|
      relation.delete_all
      sleep 10 # Throttles the delete queries
    end

[ci skip] Remove `identity.active_record`

This is removed by this commit
cf: https://github.com/rails/rails/pull/5261

Speed up code and avoid unnecessary MatchData objects