As described in the "Follow Coding Conventions" section in our
contribution guide (http://edgeguides.rubyonrails.org/contributing_to_ruby_on_rails.html#follow-the-coding-conventions)
we favor `assert_not` over `refute`.

While we don't usually make stylistic changes on it's own I opted to do
it in this case. The reason being that test cases are usually copied as
a starting point for new tests. This results in a spread of `refute` in
files that have been using it already.

Assert that the `:prefix` option of `number_to_human_size` is deprecated

Replace the giant comment in routes.rb with a link to the guides

[ci skip] Documentation: Switch around a common phrase for readability

I didn't like this method because it mutates the parameters.  Now that
the method is so small, just push it up to `initialize`

If the through class has default scopes we should skip the statement
cache.

Closes #20745.

now the `@defaults` variable doesn't need to be set before calling
`normalize_defaults`

These three options are stored in the `scope` chain outside of the
options hash.  If they are in the options hash, then someone passed them
in to `match` and they don't really do anything.  So lets remove the
code.

remove `format` from the options hash in the scope chain so that we
don't need to remove it later

this reduces the number of times we have to mutate the options hash.

This just ensures that `format` is applied to things inside the scope

Fewer objects and refactoring

Since we are always responding with an array and using `any?`, we don't
need to check if an array is empty

Now we don't have to manually remove this from the options hash since
the scope stores it outside of "options"

Remove the `options` reader from `Resource` because nobody needs to see
that hash.  Also remove mutations on the options hash in
`apply_common_behavior_for` because leaving the side effects in that
method makes it difficult to understand what is going on in the caller.

these two keys have a different merge strategy, and they also just get
removed from the options hash later in the code.  If we store them in a
separate place, then we don't need to remove them later

Eventually we don't want to expose the "options" hash from scope, only
read values from it.  Lets start by adding a reader method.

now we don't need to construct a Mapping object just to get an
ArgumentError if there is no `via` parameter provided.

We're going to try pulling this up further, and check `via` validity
sooner.  This way we don't have to do a bunch of processing on `options`
hashes only to find out that the route is incorrect

If we do the Regexp verification in a second method, then the
`split_constraints` method gets much easier.

I don't want `split_constraints` to mutate any instance variables.  That
way it's easier to move the method around and understand what it does
(it has no side effects)

I don't want to rely on mutating ivars.  This gives me more freedom when
refactoring

[ci skip] Removed link to reSRC.io - site closed

[ci skip] Fix rdoc markup

`+` doesn't work around content with spaces fallback `<tt>`.

[ci skip] Fix the indentation

[ci skip] Swap ruby -v and the installation tip