msg counter for component

Usage

settings = [
  *_options: [
    pipelines: [SpiderMan.Pipeline.Counter | {SpiderMan.Pipeline.Counter, scope}]
  ],
  ...
]

Support for all component: downloader | spider | item_processor.

Scope

• :common | [scope: :common]: save counter to common_pipeline_tid.

• :pipeline | [scope: :pipeline]: save counter to pipeline_tid.

common_pipeline_tid use by all component, pipeline_tid only use by one component.