Fix example description to match option under test
Broaden the path types for setting formatters.

By inversing the check for what a `path`, a broader range of types are
accepted:

  - `String` paths
  - `Pathname` paths
  - `File`
  - Any `IO`
  - `StringIO`
  - Custom "streams"

Do not use `IO === p` for the path check as this does not permit
`StringIO` streams[1]. Use `puts` for the `respond_to` check, instead of
the stream-y `write`, since several internal "streams" only implement
`puts` (`RaiseErrorStream` and `FileStream`).

[1] https://www.ruby-forum.com/topic/127817
Include fix in Changelog.
Merge pull request #1478 from rspec/deprecation-stream-pathname

Support `Pathname` for output streams.
Line number always takes precendence when running with filters.
Collapse two similar methods, the name is sufficient to cover both cases.
Add spec to cover preferential treatment of description match.
Merge pull request #1474 from rspec/issue-779

Line number always takes precendence when running with filters.
remove support for legacy formatters
Merge pull request #1470 from rspec/remove_legacy_formatter_support

Remove support for inherited legacy formatters [WIP]
changelog for #1470
dup formater_loader.formatters when returning from config
remove unnecessary tag
[skip ci]
changelog for #1486
[skip ci]
Merge pull request #1486 from rspec/return_formatters_dup

Dup formatters to prevent mutation
Restrict minitest to 5.x.

We're not sure yet what minitest 6.x will entail. So we're locking the
gem to a 5.x version.
Include feature spec on desired behavior.

Mark feature as `@wip` so it doesn't fail the build while the feature is
being implemented.
Replace `stdlib` with `minitest` & `test_unit`.

- Remove support for the `stdlib` expectation framework
- Include `test_unit`
- Include `minitest`
- In specs treat previous `stdlib` as `minitest`
- Attempt to require the 'minitest' gem
  - Supports minitest with Ruby 1.8.7
  - Supports minitest 5.x which is not part of stdlib
Remove wip tag.
Note behavior change in changelog.