migration and association guides: added some remarks about join tables

Allow Minitest to load plugins. Fixes #21102

Inform user to add script in correct location into the application.js manifest file [ci skip]

use it

change the warning

Fix the documentation of Hash#except method [ci skip]

fix minor problems

This reverts commit 465f0fbc.

This breaks some cases where non file / directory arguments are passed
to the runner (for example db:migrate).

I still think that we can get this to work. From what I can tell there
is no reason why db:migrate is passed along to `Minitest.run`. I'll
revert and investigate possible solutions.

Fixes #21085.

Publish the "Caching with Rails" guide

Inform user to add styles in correct location in application.css

[ci skip]

Before this patch, using `bin/rails test` with a non existing
file or directory argument would silently swallow the argument and
run the whole test suite.

After the patch the command fails with `cannot load such file --`.

Add missing assertion for test_route_with_colon_first

Update Time#advance documentation with examples [ci skip]

Fix ambiguous argument warning

encapsulate all arguments

Use #start_with? and #[] for speed

Save a string allocation inside loop

In the `tag_options` method, strings are continuously added to the
`output` string. Previously, we concatenated two strings and added the
generated string to `output`. By adding each of the strings to
`output`, one after the other, we will save the allocation of that
concatenated string.

Benchmark:

    require 'benchmark/ips'

    sep = " ".freeze

    Benchmark.ips do |x|
      x.report("string +") {
        output = ""
        output << sep + "foo"
      }
      x.report("string <<") {
        output = ""
        output << sep
        output << "foo"
      }
      x.compare!
    end

Results (Ruby 2.2.2):

    Calculating -------------------------------------
                string +    88.086k i/100ms
               string <<    94.287k i/100ms
    -------------------------------------------------
                string +      2.407M (± 5.8%) i/s -     12.068M
               string <<      2.591M (± 7.0%) i/s -     12.917M

    Comparison:
               string <<:  2591482.4 i/s
                string +:  2406883.7 i/s - 1.08x slower

While the readability may be slightly worse, the speed improvement is
significant: Twice as fast when there's no leading "/" to remove, and
over 4 times as fast when there is a leading "/".

Benchmark:

    require 'benchmark/ips'

    def match(controller)
      if controller
        if m = controller.match(/\A\/(?<controller_without_leading_slash>.*)/)
          m[:controller_without_leading_slash]
        else
          controller
        end
      end
    end

    def start_with(controller)
      if controller
        if controller.start_with?('/'.freeze)
          controller[1..-1]
        else
          controller
        end
      end
    end

    Benchmark.ips do |x|
      x.report("match") { match("no_leading_slash") }
      x.report("start_with") { start_with("no_leading_slash") }

      x.compare!
    end

    Benchmark.ips do |x|
      x.report("match") { match("/a_leading_slash") }
      x.report("start_with") { start_with("/a_leading_slash") }

      x.compare!
    end

Result (Ruby 2.2.2):

    Calculating -------------------------------------
                   match    70.324k i/100ms
              start_with   111.264k i/100ms
    -------------------------------------------------
                   match      1.468M (± 7.1%) i/s -      7.314M
              start_with      3.787M (± 3.5%) i/s -     18.915M

    Comparison:
              start_with:  3787389.4 i/s
                   match:  1467636.4 i/s - 2.58x slower

    Calculating -------------------------------------
                   match    36.694k i/100ms
              start_with    86.071k i/100ms
    -------------------------------------------------
                   match    532.795k (± 4.7%) i/s -      2.679M
              start_with      2.518M (± 5.8%) i/s -     12.566M

    Comparison:
              start_with:  2518366.8 i/s
                   match:   532794.5 i/s - 4.73x slower

correct example of button_tag [ci skip]

wrapper div has been removed in cbb91745

PostgreSQL is strict about the usage of `DISTINCT` and `ORDER BY`, which
one of the tests demonstrated. The order clause is never going to be
relevant in the query we're performing, so let's just remove it
entirely.

Add #cache_key to ActiveRecord::Relation.

[ci skip]

Add descriptions about `ActiveRecord::Base#to_param` to

* `ActionDispatch::Routing::Base#match`
* Overriding Named Route Parameters (guide)

When passes `:param` to route definision, always `to_param` method of
related model is overridden to constructe an URL by passing these
model instance to named_helper.

This is a follow up to #21008.

Add documentation to get a running custom base controller [ci skip]

Fix WARNINGS flag inside guides/Rakefile

Don't fail when checking dependencies in bin/setup script

Array#any? is slower and not the inverse of Array#empty?

```
empty_array = []
small_array = [1] * 30
bigger_array = [1] * 300

Benchmark.ips do |x|
  x.report('empty !empty?') { !empty_array.empty? }
  x.report('small !empty?') { !small_array.empty? }
  x.report('bigger !empty?') { !bigger_array.empty? }

  x.report('empty any?') { empty_array.any? }
  x.report('small any?') { small_array.any? }
  x.report('bigger any?') { bigger_array.any? }
end
```

```
Calculating -------------------------------------
       empty !empty?   132.059k i/100ms
       small !empty?   133.974k i/100ms
      bigger !empty?   133.848k i/100ms
          empty any?   106.924k i/100ms
          small any?    85.525k i/100ms
         bigger any?    86.663k i/100ms
-------------------------------------------------
       empty !empty?      8.522M (± 7.9%) i/s -     42.391M
       small !empty?      8.501M (± 8.5%) i/s -     42.202M
      bigger !empty?      8.434M (± 8.6%) i/s -     41.894M
          empty any?      4.161M (± 8.3%) i/s -     20.743M
          small any?      2.654M (± 5.2%) i/s -     13.256M
         bigger any?      2.642M (± 6.4%) i/s -     13.173M
```

Ref: https://github.com/rails/rails/pull/21057#discussion_r35902468