Improve wording in cache documentation

Allow autoloader inflectors to be swaped out

Add version awareness to rails db:system:change

Build assets automatically if necessary

In CI, these are unnecessary because done by preprocessing.
To test locally, you need to do it manually. If assets not exist, it will
fail when a run specific test, so force to build those only when necessary.

Update `multiline?` sample code [ci skip]

Corrected execution result of Enumerable#sum [ci skip]

Delegate `only` query method to relation as with `except`

Learn more about inflections[ci skip]

Update racc to latest version

racc 1.4.15 includes fixes for compiling with Ruby 2.7 since
[ruby/ruby@3d1c86a](https://github.com/ruby/ruby/commit/3d1c86a).

Before:

```
ruby -v
ruby 2.7.0dev (2019-03-07 trunk 67189) [x86_64-linux]

bundle install
...
Fetching racc 1.4.14
Installing racc 1.4.14 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

current directory:
/home/u/.rbenv/versions/2.7.0-dev/lib/ruby/gems/2.7.0/gems/racc-1.4.14/ext/racc
/home/u/.rbenv/versions/2.7.0-dev/bin/ruby -I
/home/u/.rbenv/versions/2.7.0-dev/lib/ruby/2.7.0 -r
./siteconf20190307-14242-16jzp6c.rb extconf.rb
checking for rb_ary_subseq()... yes
creating Makefile

current directory:
/home/u/.rbenv/versions/2.7.0-dev/lib/ruby/gems/2.7.0/gems/racc-1.4.14/ext/racc
make "DESTDIR=" clean

current directory:
/home/u/.rbenv/versions/2.7.0-dev/lib/ruby/gems/2.7.0/gems/racc-1.4.14/ext/racc
make "DESTDIR="
make: *** No rule to make target
'/home/u/.rbenv/versions/2.7.0-dev/include/ruby-2.7.0/defines.h', needed
by
'cparse.o'.  Stop.

make failed, exit code 2

Gem files will remain installed in
/home/u/.rbenv/versions/2.7.0-dev/lib/ruby/gems/2.7.0/gems/racc-1.4.14
for
  inspection.
  Results logged to
  /home/u/.rbenv/versions/2.7.0-dev/lib/ruby/gems/2.7.0/extensions/x86_64-linux/2.7.0-static/racc-1.4.14/gem_make.out

  An error occurred while installing racc (1.4.14), and Bundler cannot
  continue.
  Make sure that `gem install racc -v '1.4.14' --source
  'https://rubygems.org/'`
  succeeds before bundling.

  In Gemfile:
    racc
```

I've found the skewness of delegation methods between `except` and
`only` in a88b6f25.

The `only` method is closely similar with `except` as `SpawnMethods`.

https://github.com/rails/rails/blob/e056b9bfb07c4eb3bcc6672d885aadd72bec574f/activerecord/lib/active_record/relation/spawn_methods.rb#L53-L67

It is preferable both behaves the same way.

Replace “can not” with “cannot”.

This makes to ease testing `QUERYING_METHODS`.

Explicitly require rails-html-sanitizer gem in ActionText helpers

[ci skip] Fix typos

That is happened with `distinct`, and that is not only happened on MyS
L, but also on PostgreSQL, SQL Server, and Oracle.

[ci skip]

[ci skip]Fix typo:  constaint -> constraint

If the [`action_text.helper` initializer][0] runs after
`ActionController::Base` has been loaded, but before the
`rails-html-sanitizer` gem has been `require`d, then the reference to
the constant `Rails::Html` in the body of the
`ActionText::ContentHelper` module raises an `uninitialized constant`
exception.

[0]: https://github.com/rails/rails/blob/21703382393c87212c27c988420ee5c133c1aa9f/actiontext/lib/action_text/engine.rb#L31-L35

Fix including/excluding flattening

Update links and code examples in the guides to use HTTPS

Load YAML for rake tasks without parsing ERB