5.1.0

• Improve support of Active Resource objects inside fibers.

• Add support to Active Model Serializers.

• Fix error when trying to parse nil as a JSON response.

• Fix exists? to return the right value when the response code is between 200 and 206.

• Match the log level to the HTTP response code.

• Add ActiveResource::Connection.logger accessors to configure a specific logger instance for the
  connection object.

• Add ActiveResource::Base#element_url method.

• Add Active Job serialization support with Rails 6.

• Support lazy setting of configuration options.

• Use UnnamedResource when resource fails to create normally.

• Add support to Bearer Token Authorization header to connection.