add watch option for cache validation

examples/watch/.eslintrc.js

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+module.exports = {
+    "env": {
+        "browser": true,
+        "es6": true,
+        "node": true
+    },
+    "extends": "eslint:recommended",
+    "installedESLint": true,
+    "parserOptions": {
+        "ecmaFeatures": {
+            "experimentalObjectRestSpread": true,
+            "jsx": true
+        },
+        "sourceType": "module"
+    },
+    "plugins": [
+        "react"
+    ],
+    "rules": {}
+};

examples/watch/.gitignore

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+node_modules
+dist

examples/watch/README.md

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+# AutoDllPlugin Watch Example
+
+### How to install
+
+1. `git clone [email protected]:asfktz/autodll-webpack-plugin.git`
+2. `cd examples/watch`
+3. `npm install`
+4. `npm run`
+5. `open http://localhost:8080`
+
+
+### How to use
+
+1. Close devServer using ctrl + C
+2. Rerun the devServer using `npm start` to verify that cache is working
+3. Modify something in node_modules or package.json
+4. Close devServer using ctrl + C
+5. Rerun devServer using `npm start`
+6. You'll see that DLL is recompiling, cache is invalidated, and your changes should be included in the DLL bundle.
+7. Repeat