Update css-split-webpack-plugin to listen for webpack emit

[didi0613]

Issue: For IE9, css splitting before optimization, which causing an incorrect z-index reduction under production.

Proposal:

• keep the original logic
• add an listenForEmit option to the plugin to listen for webpack emit The PR added an option to the plug-in to run on emit, so it maintain backwards compatibility

[izaakschroeder]

See if you can get CI passing here @didi0613?

[izaakschroeder]

I think this is less than ideal but I understand the pragmatic reasons for having it. Seems fine to me, maybe a few tweaks.

[jchip]

@izaakschroeder another approach is do it like the CSS optimize plugin using the last call plugin, which listens to all compilation/optimize-chunks-assets event, but check for existence of CSS in assets. The approach @didi0613 took here would allow a patch release.

[izaakschroeder]

I'm fine with this @jchip @didi0613. It's not ideal but it won't blow anything up and it obviously solves a real problem. I think CI was complaining about invalid peer dependency on a module that isn't even required. Should be fixed in latest master. You can rebase and squash and should be just about good to go.

[didi0613]

@izaakschroeder Checks have passed. Please let me know if anything else i need to fix. Thank you

[izaakschroeder]

I just cleaned a few things up in your branch here https://github.com/metalabdesign/css-split-webpack-plugin/pull/21. You're still listed as the author. 😄 Available now as + css-split-webpack-plugin@0.2.4.

[izaakschroeder]

Thanks again for contributing @didi0613 @jchip 🎉