feat(stylelint-config): add @modular-css/stylelint-config package (#637)

* feat(stylelint-config): add @modular-css/stylelint-config package

Provides a basic stylelint config that can be used with the `extends` feature in stylelint to easily prevent it from barfing on modular-css features.

packages/stylelint-config/.npmignore

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+coverage/
+profiling/
+test/
+.*
+CHANGELOG.md

packages/stylelint-config/LICENSE

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+MIT License
+
+Copyright (c) 2019 Pat Cavit
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

packages/stylelint-config/README.md

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+@modular-css/stylelint-config  [![NPM Version](https://img.shields.io/npm/v/@modular-css/stylelint-config.svg)](https://www.npmjs.com/package/@modular-css/stylelint-config) [![NPM License](https://img.shields.io/npm/l/@modular-css/stylelint-config.svg)](https://www.npmjs.com/package/@modular-css/stylelint-config) [![NPM Downloads](https://img.shields.io/npm/dm/@modular-css/stylelint-config.svg)](https://www.npmjs.com/package/@modular-css/stylelint-config)
+===========
+
+<p align="center">
+    <a href="https://gitter.im/modular-css/modular-css"><img src="https://img.shields.io/gitter/room/modular-css/modular-css.svg" alt="Gitter" /></a>
+</p>
+
+Sharable stylelint config for [`modular-css`](https://m-css). By default stylelint will complain about things like `@value`, `@composes`, `composes: fooga;`, and other bits of custom modular-css syntax. This configures the relevant stylelint rules so that those bits of functionality are ignored so that you don't get a bunch of bogus warnings or errors for using modular-css.
+
+Someday it might even validate things for you, but that's a trickier proposition. For now not barfing errors/warnings everywhere is a good start.
+
+- [Install](#install)
+- [Usage](#usage)
+
+## Install
+
+```bash
+> npm i @modular-css/stylelint -D
+```
+
+## Usage
+
+Inside your [stylelint config](https://stylelint.io/user-guide/configuration/) you'll specify an [`extends`](https://stylelint.io/user-guide/configuration/#extends) property pointing to this package.
+
+```js
+{
+    "extends" : "@modular-css/stylelint-config",
+    "rules" : {
+        // ...
+    }
+}
+```

packages/stylelint-config/package.json

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+{
+  "name": "@modular-css/stylelint-config",
+  "version": "24.2.2",
+  "description": "Stylelint config to suport modular-css syntax",
+  "main": "./stylelint.js",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/tivac/modular-css.git",
+    "directory": "packages/stylelint"
+  },
+  "bugs": {
+    "url": "https://github.com/tivac/modular-css/issues"
+  },
+  "author": "Pat Cavit <npm@patcavit.com>",
+  "homepage": "https://m-css.com",
+  "license": "MIT",
+  "publishConfig": {
+    "access": "public"
+  },
+  "keywords": [
+    "stylelint",
+    "stylelint-config",
+    "css",
+    "css-modules",
+    "modular-css",
+    "postcss"
+  ]
+}

packages/stylelint-config/stylelint.js

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+"use strict";
+
+module.exports = {
+    rules : {
+        "at-rule-no-unknown" : [ true, {
+            ignoreAtRules : [
+                "value",
+                "composes"
+            ]
+        }],
+
+        "declaration-block-no-duplicate-properties" : [ true, {
+            ignoreProperties : [
+                "composes"
+            ]
+        }],
+
+        "property-no-unknown" : [ true, {
+            ignoreProperties : [
+                "composes"
+            ]
+        }],
+
+        "selector-pseudo-class-no-unknown" : [ true, {
+            ignorePseudoClasses : [
+                "global",
+                "external",
+            ]
+        }],
+    }
+};