Added

• GitHub Actions build status badge in README.md
• Support for custom date formats in Retry-After header via new retry_after_date_format option
• max_allowable_timeout_secs option to set a ceiling on the maximum time the client is willing to wait between requests
• Support for Guzzle 7 class-based static methods

Changed

• Removed unnecessary comments
• Name of Github Action to Github Build

Removed

• .travis.yml build support (switched to Github Actions)