Add removeOriginalExtension option

[aszx87410]

This PR add a new option called removeOriginalExtension.

When images converted to WebP on the fly, .webp was append to the filename. For example, test.png became test.png.webp. If you want to have only one filename extension like test.webp, you can set this option to true.

The motivation is because for some CDN services(like Azure CDN), it decides response header content-type by filename and it failed to recognize multiple filename extensions like .png.webp, so the content-type will be default value which is application/octet-stream.

There is no option to disable this behavior for now so I purpose this PR. Please let me know if there is any problem, and thanks for making this awesome library 😄

[codecov]

Codecov Report

Merging #158 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #158   +/-   ##
=======================================
  Coverage   88.42%   88.42%           
=======================================
  Files          13       13           
  Lines         190      190           
  Branches       46       46           
=======================================
  Hits          168      168           
  Misses         16       16           
  Partials        6        6           

Impacted Files	Coverage Δ
lib/config.js	100.00% <ø> (ø)
lib/loaders/webp-loader.js	100.00% <ø> (ø)

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[cyrilwanner]

Thank you very much for this contribution!
Adding that option makes sense, I may even make this the default one with the next major version.

Will publish this change to npm as a patch in a few minutes.

[aszx87410]

Thanks for the promptly response and the new patch, I am glad to contribute. And I want to add one thing I mentioned above about content type. I upgrade my project today and turns out the Azure CDN still can't recognize the file with .webp extension, so I think maybe it's more about uploading issue, not about filename extension.

Anyway, I think it's still great to add this option to keep filename pure. Thanks for the quick response again!