Fix spacing issue
4.0 Release notes should point to 4.0 Changelog
Be assertive about adding `[ci skip]` message
`attibutes` => `attributes`
`implemention` => `implementation`
Example of Join models

In the example of join models, there are five models but in the explanation only consider Category, Post, Comment and Guest.
Client.exists?(1,2,3) and Client.exists?([1,2,3]) does not work

The right command for doing that is Client.exists?id:[1,2,3]
Exists does not work like find method, in find method you can do Person.find(1, 2, 6) or Person.find([7, 17]) but not Person.exists?(1,2,3) or Person.exists?([1,2,3])
Review the changes made on 90155b4e28a3887dce9428e9df150ede3d6c7465
added # or comment
Cleanup of excerpt helper

* replaced String concatenation by joining
* separator has default value to '', even it is nil
Blacklist refferenced in docs is actually whitelist
The docs refference a blacklist, but really what's being described
is a whitelist. Anything that matches the constraint gets through to
the path.
Change documentation to consistently refer to the same object
The documentation in this section is referring to a profile,
so the resource that's created should probably also be a
profile of some sort.
html generated for a search form

There's a div that is generated in rails for a default search form and is not includen in the example.
[ci skip] Add missing setting locale code snippet.

This is for 3 Internationalizing your Application of i18n.md.

Missing the code as mentioned in 2.3, setting locale.

Without this, the example to add config/locales/pirate.yml will not work.
[ci skip] Fix links in section 5.3 of i18n.md

Now all links point to the correct line number.
Plural of Deer not deer

Change the plural of Deer word in the naming conventions
Perf: avoid dupes add fallback logic for coders
Reduce allocations when extracting AR models
Relation#merge should not lose readonly(false) flag.

The original code ignores the `false` value because `false.blank? # => true`.
Fix FileStore#cleanup to no longer rely on missing each_key method