Added some failing tests where the JSON encoder is not resolving as_json correctly
Expanded coverage on JSON encoding
Removed support for encoding BigDecimal as a JSON number

This is because the new encoder will no longer support encode_json.
Therefore our only choice is to return `to_i` or `to_s` in
`BigDecimal#as_json`. Since casting a BigDecimal to an integer is
most likely a lossy operation, we chose to encode it as a string.

Support for encoding BigDecimal as a string will return via the
`activesupport-json_encoder` gem.
Removed the Ruby encoder and switched to using the JSON gem

Got all the tests passing again.

Support for `encode_json` has been removed (and consequently the
ability to encode `BigDecimal`s as numbers, as mentioned in the
previous commit). Install the `activesupport-json_encoder` gem
to get it back.
Make the JSON encoder pluggable
Process::Status should get a :nodoc: [ci skip]
Be explicit and use the actual unicode sequence
More typo fixes
Merge pull request #12183 from chancancode/json_encoder_refactor

JSON encoder refactor
Merge pull request #13061 from laurocaetano/fix-uniqueness-validation-for-aliased-attribute

Fix bug when validating the uniqueness of an aliased attribute.
Conflicts:
	activerecord/CHANGELOG.md
Link for "New Post" is added in Getting Started guide [ci skip]

- Earlier(line number 862) it is said to add <%= link_to 'New post', new_post_path %> on posts index page before table tag. But when posts index page html is shown, "New Post" link is missing.
So aaded "New Post" link in this commit
Dropped yajl from Gemfile
Requires JSON gem version 1.7.7 or above as it contains an important
security fix.
Deprecated Numeric#{ago,until,since,from_now}

The user is expected to explicitly convert the value into an
AS::Duration, i.e. `5.ago` => `5.seconds.ago`

This will help to catch subtle bugs like:

  def recent?(days = 3)
    self.created_at >= days.ago
  end

The above code would check if the model is created within the last 3
**seconds**.

In the future, `Numeric#{ago,until,since,from_now}` should be removed
completely, or throw some sort of errors to indicate there are no
implicit conversion from `Numeric` to `AS::Duration`.

Also fixed & refactor the test cases for Numeric#{ago,since} and
AS::Duration#{ago,since}. The original test case had the assertion
flipped and the purpose of the test wasn't very clear.
[ci skip] used new syntax for scopes
Merge pull request #13070 from kuldeepaggarwal/documentation-updation

[ci skip] used new syntax for scopes
[ci skip]removed obsolete information about `options` parameter in create method
Merge pull request #13071 from kuldeepaggarwal/documentation-updation

[ci skip]removed obsolete information about `options` parameter in create method
Merge pull request #13069 from chancancode/json_gem_version

Requires JSON gem version 1.7.7 or above as it contains an important security fix.
Merge pull request #13068 from chancancode/drop_yajl_from_gemfile

Dropped yajl from Gemfile