Print distinct end line to support better output error parsing in watch mode

[webpack-bot]

Do you want to request a feature or report a bug?

A feature.

What is the current behavior?

The output consists of various information regarding the included bundles, time taken, etc., followed by warnings and errors if there are any, but nothing follows that, indicating that the compilation is fully completed.

If the current behavior is a bug, please provide the steps to reproduce.

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What is the expected behavior?

Print something unique like --- Compilation completed. --- so the output of one cycle can be found between the Hash: XXXXX and that line. Optionally a similar line could be added before each compilation (e.g. --- Starting compilation. ---).

If this is a feature request, what is motivation or use case for changing the behavior?

Support editors and development tools in aggregating and highlighting issues in code.

Please mention other relevant information such as the browser version, Node.js version, webpack version and Operating System.

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This issue was moved from webpack/webpack#6002 by @sokra. Orginal issue was by @brunnerh.

This sounds like a useful opt-in feature.