Do you have any plans to support parameter like ignore_failure?

[ryysud]

If the task of digdag-slack fails, subsequent tasks are not executed as follows.

$ cat sample.dig
_export:
  plugin:
    repositories:
      - https://jitpack.io
    dependencies:
      - com.github.szyn:digdag-slack:0.1.4
  webhook_url: mistake_url
  workflow_name: slack
  ENV: develop

+first_task:
  echo>: "run first task!"
  _check:
    slack>: templates/success.yml

+second_task:
  echo>: "run other tasks!"

$ digdag run -a sample.dig
2017-11-30 05:39:29 +0000: Digdag v0.9.21
2017-11-30 05:39:32 +0000 [WARN] (main): Reusing the last session time 2017-11-30T00:00:00+00:00.
2017-11-30 05:39:32 +0000 [INFO] (main): Using session /root/digdag-slack/.circleci/.digdag/status/20171130T000000+0000.
2017-11-30 05:39:32 +0000 [INFO] (main): Starting a new session project id=1 workflow name=sample session_time=2017-11-30T00:00:00+00:00
2017-11-30 05:39:34 +0000 [INFO] (0016@[0:default]+sample+first_task): echo>: run first task!
run first task!
2017-11-30 05:39:36 +0000 [INFO] (0016@[0:default]+sample+first_task^check): slack>: templates/success.yml
2017-11-30 05:39:37 +0000 [ERROR] (0016@[0:default]+sample+first_task^check): Task failed with unexpected error: unexpected url: mistake_url
java.lang.IllegalArgumentException: unexpected url: mistake_url
	at okhttp3.Request$Builder.url(Request.java:143)
	at io.digdag.plugin.slack.SlackOperatorFactory$SlackOperator.postToSlack(SlackOperatorFactory.java:81)
	at io.digdag.plugin.slack.SlackOperatorFactory$SlackOperator.runTask(SlackOperatorFactory.java:69)
	at io.digdag.util.BaseOperator.run(BaseOperator.java:35)
	at io.digdag.core.agent.OperatorManager.callExecutor(OperatorManager.java:312)
	at io.digdag.cli.Run$OperatorManagerWithSkip.callExecutor(Run.java:694)
	at io.digdag.core.agent.OperatorManager.runWithWorkspace(OperatorManager.java:254)
	at io.digdag.core.agent.OperatorManager.lambda$runWithHeartbeat$2(OperatorManager.java:137)
	at io.digdag.core.agent.LocalWorkspaceManager.withExtractedArchive(LocalWorkspaceManager.java:25)
	at io.digdag.core.agent.OperatorManager.runWithHeartbeat(OperatorManager.java:135)
	at io.digdag.core.agent.OperatorManager.run(OperatorManager.java:119)
	at io.digdag.cli.Run$OperatorManagerWithSkip.run(Run.java:676)
	at io.digdag.core.agent.MultiThreadAgent.lambda$null$0(MultiThreadAgent.java:127)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
2017-11-30 05:39:39 +0000 [INFO] (0016@[0:default]+sample^failure-alert): type: notify
error:
  * +sample+first_task^check:
    unexpected url: mistake_url (illegal argument)

Task state is saved at /root/digdag-slack/.circleci/.digdag/status/20171130T000000+0000 directory.
  * Use --session <daily | hourly | "yyyy-MM-dd[ HH:mm:ss]"> to not reuse the last session time.
  * Use --rerun, --start +NAME, or --goal +NAME argument to rerun skipped tasks.

I would like to allow subsequent tasks to be executed even If the task of digdag-slack fails.
Do you have any plans to support parameter like ignore_failure ?