be more specific about csrf token and ajax - not whitelisted outside of jquery-rails [ci skip]
Save has_one associations only if record has changes

Prevents save related callbacks such as `after_commit` being
triggered when `has_one` objects are already persisted and have no
changes.
Only use BINARY for mysql case sensitive uniqueness check when column has a case insensitive collation.
`find_in_batches` now returns an `Enumerator` when called without a block, so that it
can be chained with other `Enumerable` methods.
Fix breakage in XmlMini

- Boolean parsing breaks on non strings (i.e. integer 1|0)
- Symbol parsing breaks on non strings.
- BigDecimal parsing breaks due to missing require.
- Update changelog.
Fixed typo [ci skip]

singular is more suited to
change to "check out"
e-mail => email, and subject/verb agreement
add punctuation
Remove duplicate configuration option for ActiveSupport [ci skip]

Fixes rails/rails#13732
psql implementation of #index_name_exists?
`requies` => `requires`
`easiy` => `easy`
`framwork` => `framework`
Remove old comments about suppressing warnings.
Replace Post with Article in getting started guide [ci skip]

- Used Article model instead of Post as it may confuse with 'post'
  requests
- Tried to wrap the guide to 80 chars lines as much as possible.
- Removed unused image
- Fixes #13764
Correct grammar from '... allowing both thread web servers ...' to '... allowing both threaded web servers ...'.
Merge pull request #13844 from Alamoz/config_grammar

thread -> threaded [ci skip]
Add the ability to intercept emails before previewing

To support the ability for tools like CSS style inliners to operate on emails
being previewed this commit adds a hook in a similar fashion to the existing
delivery interceptor hook, e.g:

  class CSSInlineStyler
    def self.previewing_email(message)
      # inline CSS styles
    end
  end

  ActionMailer::Base.register_preview_interceptor CSSInlineStyler

Fixes #13622.
Don't use a class_attribute for ActionMailer::Base.preview_path

Since preview_path is read from ActionMailer::Base when previewing, subclasses
can’t change it so don’t there's no need for the extra overhead imposed by using it.