Modify the Hash#assert_valid_keys error message so that it shows the valid keys. Also, show the wrong value as it was entered.

{ :failore => "stuff", :funny => "business" }.assert_valid_keys([ :failure, :funny ])
=> ArgumentError: Unknown key: failore
{ 'failore' => "stuff", :funny => "business" }.assert_valid_keys([ :failure, :funny ])
=> ArgumentError: Unknown key: failore

{ 'failore' => "stuff", :funny => "business" }.assert_valid_keys([ :failure, :funny ])
=> ArgumentError: Unknown key: "failore". Valid keys are: :failure, :funny

{ :failore => "stuff", :funny => "business" }.assert_valid_keys([ :failure, :funny ])
=> ArgumentError: Unknown key: :failore. Valid keys are: :failure, :funny

Conflicts:
	activerecord/CHANGELOG.md

Closes #11624.

Use the already existing strings instead of creating a new one each time
just to test if it responds to the methods.

Improve Module#delegate documentation to tell that delegate don't work with private or protected methods. [ci skip]

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.

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.

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.

should also call #as_json on the children without options (instead of
nil)

Example:

    class A
      cattr_reader(:defr) { 'default_reader_value' }
    end
    A.defr # => 'default_reader_value'

Previously, calling `::JSON.{generate,dump}` sometimes causes
unexpected failures such as intridea/multi_json#86.

`::JSON.{generate,dump}` now bypasses the ActiveSupport JSON encoder
completely and yields the same result with or without ActiveSupport.
This means that it will **not** call `as_json` and will ignore any
options that the JSON gem does not natively understand. To invoke
ActiveSupport's JSON encoder instead, use `obj.to_json(options)` or
`ActiveSupport::JSON.encode(obj, options)`.

According to our guideline, we leave 1 space between `#` and `=>`, so we
want `# =>` instead of `#=>`.

Thanks to @fxn for the suggestion.

[ci skip]

Ruby 2.0.0p247
Rehearsal ---------------------------------------
old  10.670000   0.150000  10.820000 ( 10.822651)
new   8.520000   0.050000   8.570000 (  8.571825)
----------------------------- total: 19.390000sec

          user     system      total        real
old  10.620000   0.170000  10.790000 ( 10.790409)
new   8.570000   0.110000   8.680000 (  8.686051)

In #12203, the JSON core extensions were moved into the `core_ext`
folder. Unfortunately, there are some corresponding requires that
were left behind. The problem is partially addressed in #12710, this
commit fixes the rest.

See [1] for why this is not a good idea.

As part of this refactor, circular reference protection in as_json has
been removed and the corresponding error class has been deprecated.

As discussed with @jeremy, circular reference error is considered
programmer errors and protecting against it is out of scope for
the encoder.

This is again based on the excellent work by @sergiocampama in #11728.

[1]: https://github.com/intridea/multi_json/pull/138#issuecomment-24468223

So strings can be humanized without being capitalized:

    'employee_salary'.humanize                    # => "Employee salary"
    'employee_salary'.humanize(capitalize: false) # => "employee salary"

JSON.{dump,generate} offered by the JSON gem is not compatiable with
Rails at the moment and can cause a lot of subtle bugs when passed
certain data structures. This changed all direct usage of the JSON gem
in internal Rails code to always go through AS::JSON.{decode,encode}.

We also shouldn't be implementing `to_json` most of the time, and
these occurances are replaced with an equivilent `as_json`
implementation to avoid problems down the road.

See [1] for all the juicy details.

[1]: intridea/multi_json#138 (comment)

These methods now takes the same options as Hash#as_json, for example:

    struct = Struct.new(:foo, :bar).new
    struct.foo = "hello"
    struct.bar = "world"
    json = struct.as_json(only: [:foo]) # => {foo: "hello"}

This is extracted from PR #11728 from @sergiocampama, see also the
discussion in #11460.

Added Numeric#in_milliseconds, like 1.hour.in_milliseconds, so we can feed them to JavaScript functions like getTime().

Same as 4d4ff531

Same as #12710 but for the time module this time. This time it should
fix the Active Model test suite in isolation avoiding a TypeError to
be raised about the superclass of the DateTime object.