Svelte preprocess support

[tivac]

Adds both modular-css-svelte for usage with svelte.preprocess() and modular-css-svelte/rollup for usage with rollup-plugin-svelte.

Allows for writing modular-css within <style> tags in a svelte component!

<h1 class="{{css.title}}">Hello</h1>
<div class="{{comparison ? css.one : css.two}}">Ok</div>

<style>
.title {
    composes: otherClass from "./other-file.css";
    composes: global(anotherClass);
}

.one {
    color: red;
}

.two {
    color: blue;
}
</style>

See README.md in PR for all usage examples.