v0.1.6

added group_fail_limits and skip_unspecified_group_on_failure;

• The group_fail_limits option allows you to specify the maximum number of failed tasks for a group before the runner skips the rest of the waiting tasks in a group.
• The skip_unspecified_group_on_failure option sets the fail limit to 1 for all groups which do not have a group_fail_limit specified.