Make Sass implementation agnostic ( supporting dart-sass )

[fsubal]

Resolves: https://github.com/fetch/node-sass-asset-functions/issues/16

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I made this library to be sass-implementation agnostic, that means, add support for dart-sass.

With these changes, node-sass-asset-functions now accepts implementation option ( which excepts require('node-sass') or require('sass'), and when absent it will be implicitly node-sass )

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For some reason the test is not passing ( Maybe dart-sass cannot read file correctly, even though the path looks correct ), which is now I'm searching why... Help wanted by someone.

[marlonmarcello]

Love this, can we get it merged @koenpunt ?

[ghost]

hey folks, can this PR get merged in? would be super helpful since node-sass is basically decrepit at this point

[ghost]

for those who want to install this now

npm i --save-dev fetch/node-sass-asset-functions#pull/17/head

"devDependencies": {
  "node-sass-asset-functions": "github:fetch/node-sass-asset-functions#pull/17/head",
}

[koenpunt]

I've released a new version to npm that replaces node-sass with sass (Dart Sass). Development will continue in this fork: https://github.com/koenpunt/node-sass-asset-functions