Change double quotes to single quotes in guide

Remove unneeded `@column_types` instance variable

/cc @sgrif

Remove old deprecation warning

This was used more previously, but other uses have been removed.

Add missing test cases for `attribute_names` instance method

`reload` should fully reload attributes

There is a class method with the same name that is tested, but not the
instance method.

`reload` is meant to put a record in the same state it would be if you
were to do `Post.find(post.id)`. This means we should fully replace the
attributes hash.

This has been around for a couple of versions now, a `NoMethodError`
should suffice at this point.

[ci skip] Added missing colon in asset manifest JSON

Create with_env helper for tests.

Return a null object from `AttributeSet#[]`

Move `attributes` to the `AttributeSet` object.

Add missing test cases for `attribute_method?`

Use with_parse_json_times helper in tests.

Avoid hardcoded magic number in test teardown.

Improve consistency

[ci skip] Add Tip for change_column_null and change_column_default in guides

Make dependencies.rb add a name to NameError

The :singleton-method: directive is printed in the docs.
This directive is not necessary as the method is documentable just fine.

Add to guides app and helper objects on command line

Fix state leak.

Remove extra list item element in engine guide

Cleaning up the list items that detail what an engines `--full` option
generates. Joining a multiline multi list item into a multiline single
list item.

[ci skip]

Don't save through records twice

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/test/cases/associations/has_many_through_associations_test.rb

ErrorsController shouldn't inherit ApplicationController, but ActionController

Always update counter caches in memory when adding records