use webpacks public path instead of window.baseUrl

[ggarek]

As for version 3.0.3 there is a problem with resolving sprite paths at runtime.
It is necessary to consider webpack's public path at runtime to build a proper url for current runtime environment. The path can be accessed as __webpack_public_path__ in the chunk entry file.

It is the case when the asset path is not known statically (at build time) rather at runtime.

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This #106 may be related issue, but it is not about webpack, but some plugin (vuejs loader i guess). Because webpack does not have assetsPublicPath.

[ggarek]

i think this fix makes window.baseUrl magic redundant. But it is also a breaking change, so it must be mentioned in the change log.

[ggarek]

Renamed the issue, because it is all about using public path provided by webpack in runtime instead of another global variable.

[ggarek]

The PR was merged. There is no need to set window.baseUrl anymore.