To avoid name and department clash issues, RuboCop decided to grant each
extension its own department.
For those cops that already have the department matching the extension
name, no changes are needed.

More info rubocop/rubocop#8490

The changed cop names are:

* `Capybara/CurrentPathExpectation` -> `RSpec/Capybara/CurrentPathExpectation`
* `Capybara/FeatureMethods` -> `RSpec/Capybara/FeatureMethods`
* `Capybara/VisibilityMatcher` -> `RSpec/Capybara/VisibilityMatcher`
* `FactoryBot/AttributeDefinedStatically` -> `RSpec/FactoryBot/AttributeDefinedStatically`
* `FactoryBot/CreateList` -> `RSpec/FactoryBot/CreateList`
* `FactoryBot/FactoryClassName` -> `RSpec/FactoryBot/FactoryClassName`
* `Rails/HttpStatus` -> `RSpec/Rails/HttpStatus`

Add an uber-department

Release v2.0.0-pre, compatible with RuboCop v1.0

Only dots are used when separating versions in Rubygems.

Why?

 - it was slow #925 (comment)
 - it ignored non-describe top-level example groups #925 (comment)

`TopLevelGroup` is a modern replacement for `TopLevelDescribe`.

Examples how to migrate cops from TopLevelDescribe to TopLevelGroup:

 - #932
 - #977

Remove old Cop baseclass

Retire TopLevelDescribe

Fixes #938

Retire RSpec/InvalidPredicateMatcher

This moves several files to a new `mixins/` folder. I was going to add
some new macros, per [this comment][1], but thought it might clutter
things up a bit to put them in the root folder. I thought of adding a
`macros/` folder, but decided to emulate the [rubocop source][2]
instead.

[1]: #934 (comment)
[2]: https://github.com/rubocop-hq/rubocop/tree/master/lib/rubocop/cop/mixin

* Add shared context for all cop specs.
* Remove redundant `config` metadata for cop specs.
* Remove redundant `cop` subjects from cop specs.

Fix find_all_in_scope method docs

Add mixins folder

Use config context for all cop specs

'autocorrect' shared example group does not pass a correct file name to
the cop, and if this cop is tweaked to only inspect factories, this spec
fails because the default file name/path is skipped, since it's not a
factory path.

Refactor a spec

    lib/rubocop/cop/rspec/multiple_expectations.rb:73:32: W: Lint/ToEnumArguments: Ensure you correctly provided all the arguments.
              expectations_count = to_enum(:find_expectation, node).count
                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

We'd still love to use OUR new cops while working on our codebase, let's
see how this option works when set under RSpec namespace when we
introduce the first pending cop.

Stop using newly added cops

We have had problems with it:
 - it was slow
 - it is a non-standard extension of RuboCop's config
 - Include option exists
 - department-specific (e.g. FactoryBot) config was ignored

Remove relevance detection code

RSpec aliases runtime matchers

The customization is now made via .rubocop.yml configuration, i.e.:

    RSpec:
      Language:
        Includes:
          Example:
          - it_has_special_behavior

…tomization

Drop RSpec/EmptyExampleGroup customization

Enable pending cop(s)

It reads nicer, and `flog` agrees. Before:

❯ flog lib/rubocop/cop/rspec/mixin/top_level_group.rb
    29.7: flog total
     5.0: flog/method average

     9.8: RuboCop::Cop::RSpec::TopLevelGroup#top_level_nodes lib/rubocop/cop/rspec/mixin/top_level_group.rb:36-44
     7.6: RuboCop::Cop::RSpec::TopLevelGroup#on_new_investigation lib/rubocop/cop/rspec/mixin/top_level_group.rb:10-16
     4.9: RuboCop::Cop::RSpec::TopLevelGroup#top_level_groups lib/rubocop/cop/rspec/mixin/top_level_group.rb:20-22

After:

❯ flog lib/rubocop/cop/rspec/mixin/top_level_group.rb
    25.8: flog total
     4.3: flog/method average

     7.2: RuboCop::Cop::RSpec::TopLevelGroup#top_level_nodes lib/rubocop/cop/rspec/mixin/top_level_group.rb:35-44
     6.3: RuboCop::Cop::RSpec::TopLevelGroup#on_new_investigation lib/rubocop/cop/rspec/mixin/top_level_group.rb:10-15
     4.9: RuboCop::Cop::RSpec::TopLevelGroup#top_level_groups lib/rubocop/cop/rspec/mixin/top_level_group.rb:19-21

Add v2 update docs

Use `case` instead of `if`

- Add explicit dependency on rubocop-ast >= 1.1.0.
- Rename the "Change log" to "Changelog".
- Remove mention of "potentially breaking" changes. All changes between
  1.x and 2.0 should be regarded as potentially breaking, so no need to
  highlight one over the rest.
- Link to the upgrade document from README.