DRGN-93 Add testing and make prefixes configurable

.vscode/settings.json

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+{
+    "typescript.tsdk": "node_modules/typescript/lib"
+}

README.md

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 This [import-sort](https://github.com/renke/import-sort) is based on [import-sort-style-module](https://github.com/renke/import-sort/tree/master/packages/import-sort-style-module).
 
-```js
-// Absolute modules with side effects (not sorted because order may matter)
-import 'a';
-import 'c';
-import 'b';
-
-// Relative modules with side effects (not sorted because order may matter)
-import './a';
-import './c';
-import './b';
-
-// Third-party modules sorted by name
-import aa from 'aa';
-import bb from 'bb';
-import cc from 'cc';
-// Modules from the Node.js "standard" library sorted by name
-import { readFile, writeFile } from 'fs';
-import * as path from 'path';
-// First-party modules sorted by "relative depth" and then by name
-import aaa from '../../aaa';
-import bbb from '../../bbb';
-import aaaa from '../aaaa';
-import bbbb from '../bbbb';
-import aaaaa from './aaaaa';
-import bbbbb from './bbbbb';
+## Installation
+
+- Install with `npm i -D @leanix/import-sort-style`
+- If used with Prettier, install `npm i -D prettier-plugin-import-sort@0.0.3` for Prettier@v1 and `npm i -D prettier-plugin-import-sort` for Prettier@v2
+
+## Configuration
+
+- Add a configuration like the following to your package.json to specify the parser (which may need to be installed separately) and the corresponding extensions:
+
+```
+"importSort": {
+  ".js, .ts": {
+    "style": "@leanix/import-sort-style",
+    "parser": "typescript",
+    "options": {
+      "prefixes": [
+        "@app",
+        "@lib"
+      ]
+    }
+  }
+}
 ```
+- The list of local prefixes/aliases is optional. 
+
+## Sort order
+
+The order of imports is:
+
+1. Third-party modules with side effects are not sorted because order may matter, e.g. `import 'polyfills';`
+2. Local, absolute modules with side-effects are not sorted because order may matter, e.g. `import '@app/polyfills';`
+3. Local, relative modules with side effects are not sorted because order may matter, e.g. `import './polyfills';`
+4. Third-party modules are sorted by name, e.g. `import { endOfMonth } from 'date-fns';`
+5. Built-in Node.js modules are sorted by name, e.g. `import * as fs from 'fs';`
+6. Local, absolute modules are sorted by the prefix-order provided and then by name `import { LIMIT } from '@app/app.constants';`
+7. Local, relative modules are sorted by "relative depth" and then by name `import { LIMIT } from './app.constants';`
+
+See the [tests](./test/main.spec.ts) for more examples.

jest.config.js

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+module.exports = {
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+};