Allow default to be configured for Enum

Also fix the language identifier for one JavaScript example.

Use correct grammar in Rails 5.0 upgrade section [ci-skip]

```ruby
class Book < ActiveRecord::Base
  enum status: [:proposed, :written, :published], _default: :published
end

Book.new.status # => "published"
```

Fix typo s/delegates/delegate/

[ci skip]

fix grammar in active support docs [ci-skip]

Add Active Record Marshal forward compatibility tests

Save an allocation in visit CAT

More consistent usage of version option for commands in guides [skip ci]

In the getting started guide intro section both `-v` and `--version` are used:

    $ ruby -v
    $ sqlite3 --version
    $ node --version
    $ yarn -v
    $ rails --version

Both ruby and yarn support `--version` as well, but sqlite3 does not
support `-v`.

For consistency use `--version` option for `ruby` and `yarn` commands.

Save a string allocation in visit_STAR

Use appropriate code fences [ci skip]

Follow-up to #39620.

This commit changes a few overlooked code fences to `bash`, and changes
a few IRB session snippets to be only Ruby code with a `ruby` fence.

Include warning about S3 timeout behavior [ci skip]

Replace javascript highlighting in guides with Rouge [ci skip]

Replace javascript highlighting using Prism with the Rouge markdown
highlighter. Uses the github theme.

Docs: config.hosts: details re: regexp anchors

Type cast extra select for eager loading

It is not a big issue for common types, since type casting in master
branch is much improved, but strictly speaking eager loading should
respect column types from database like as `find_by_sql` also does.

https://github.com/rails/rails/blob/97c34a55fa0f4e8d51504bd137f6e82155336d9a/activerecord/lib/active_record/querying.rb#L46-L52

Fixes #39605.

fix misleading section on associations guide

[ci skip]

Remove broken responsive-tables JS, improving mobile readability & accessibility [ci skip]

Add link to forum

In addition remove SO link

Follow up to https://github.com/rails/homepage/pull/140

[CI skip]

Added docs for client-side logger

Change default HTTP status to 308 for ActionDispatch::SSL.