4.1.0

This is a backwards compatible, minor release.

• In the Model's Meta, you may now provide an AWS session token, which is mostly useful for assumed roles (#700):

  sts_client = boto3.client("sts")
  role_object = sts_client.assume_role(RoleArn=role_arn, RoleSessionName="role_name", DurationSeconds=BOTO3_CLIENT_DURATION)
  role_credentials = role_object["Credentials"]
  
  class MyModel(Model):
    class Meta:
      table_name = "table_name"
      aws_access_key_id = role_credentials["AccessKeyId"]
      aws_secret_access_key = role_credentials["SecretAccessKey"]
      aws_session_token = role_credentials["SessionToken"]
  
    hash = UnicodeAttribute(hash_key=True)
    range = UnicodeAttribute(range_key=True)

• Fix warning about inspect.getargspec (#701)
• Fix provisioning GSIs when using pay-per-request billing (#690)
• Suppress Python 3 exception chaining when "re-raising" botocore errors as PynamoDB model exceptions (#705)