Add support for language settings and search parameter

[necocen]

Pull Request

Related issue

Fixes #611

What does this PR do?

• Added locales parameter and with_locales method to SearchQuery struct
• Added localized attributes related methods to Index and Settings
• Added tests
• Added code samples
  • search_parameter_reference_locales_1
  • get_localized_attribute_settings_1
  • update_localized_attribute_settings_1
  • reset_localized_attribute_settings_1

PR checklist

Please check if your PR fulfills the following requirements:

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

Thank you so much for contributing to Meilisearch!