Support error_ignore for a task call.

[trulede]

Support task calls with ignore_error.

• Parse ignore_error into the cmd object for task calls.
• Handle the error condition after a task call, ignoring if error_ignore was set.

fixes #363

Example task definition

version: "3"

tasks:
  bad:
    cmds:
      - exit 1
  default:
    cmds:
      - task: bad
        ignore_error: true
      - echo hello