Add new Lint/ConstantOverwrittenInRescue cop

[ydah]

This PR is add a new cop.
Checks for overwriting an exception with an exception result by use rescue =>.

@example

# bad
begin
  something
rescue => StandardError
end

# good
begin
  something
rescue StandardError
end

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• [-] Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.

[pirj]

Wow!
Just to show the scale of destruction:

> E=Class.new(StandardError)
> begin; raise E; rescue => E; end

(pry):2: warning: already initialized constant E
(pry):1: warning: previous definition of E was here

> E
#<E: E>

😱

Frankly, it looks like a Ruby bug or a deficiency.

In any case, thanks for the cop! 👏

[bbatsov]

I'd expand on the documentation here and add some explanation that people what people wrote vs what they meant to write.

[ydah]

Documentation has been expanded to include additional explanations.

[bbatsov]

I like the cop, we just need to expand a bit the docs and the examples.

[pirj]

I'd go with ConstantOverwrittenInRescue for the cop name.

[ydah]

@pirj Thank you so much.
ConstantOverwrittenInRescue I think it is a good Cop name. I changed the cop name :)

[bbatsov]

Looks good. Thanks!