Implements show ranking scores in search query

[massijay]

Pull Request

Related issue

Fixes #458

What does this PR do?

• Implements show ranking scores in search query
• Does not implement a user friendly way to retrieve the score in the response (impossible to do without making breaking changes, see also Using _Formatted value when searching is not user friendly #315, SearchResult is badly shaped #426) users have to add the field in their classes themselves

PR checklist

Please check if your PR fulfills the following requirements:

• Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
• Have you read the contributing guidelines?
• Have you made sure that the title is accurate and descriptive of the changes?

Thank you so much for contributing to Meilisearch!

[curquiza]

thank you @massijay

bors merge

[meili-bors]

Merge conflict.

[curquiza]

bors merge

[meili-bors]

Build succeeded:

• format-check
• integration-tests