Added an additional optional variadic parameter for NewRetryMiddleware. The parameter accepts a slice of first-level functions that accepts an error argument and return boolean value. Users can specify the function(s) that they want for stopping retry middleware from retrying.
Added an additional optional variadic parameter for NewRetryMiddleware. The parameter accepts a slice of first-level functions that accepts an error argument and return boolean value. Users can specify the function(s) that they want for stopping retry middleware from retrying.
closes #94