Add Joy Joy demo

Demo detects and shows Joy-Cons in the browser with a graphic of the
button/joystick usage.

There is also an onboarding page to show how to connect a Joy-Con.

This was bootstrapped from `create-react-app`.

README.md

@@ -2,4 +2,6 @@
 
 A [Joy-Con](https://en.wikipedia.org/wiki/Joy-Con) game controller library for the browser. Built using the [Gamepad API](https://developer.mozilla.org/en-US/docs/Web/API/Gamepad_API).
 
+To see the library in action, see the [demo](./demo) folder.
+
 To see the source code, look in [src/joy-joy](./src/joy-joy).

demo/.gitignore

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+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+/.pnp
+.pnp.js
+
+# testing
+/coverage
+
+# production
+/build
+
+# misc
+.DS_Store
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*

demo/.nvmrc

@@ -0,0 +1 @@
+8.16.0

demo/README.md

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+# Joy Joy demo
+
+A demo of the [Joy Joy library](../src/joy-joy).
+
+This project was bootstrapped with [Create React App](https://github.com/facebook/create-react-app).
+
+## Development
+
+- Install [nvm](https://github.com/creationix/nvm)
+- Use correct node version
+
+        nvm use
+
+- Go to [library folder](../../src/joy-joy) and run instructions
+- Install dependencies in this folder
+
+        npm install
+
+- Run with `npm start`. Open [http://localhost:3000](http://localhost:3000) to view it in the browser.
+
+  The page will reload if you make edits.<br>
+  You will also see any lint errors in the console.
+
+### Logging
+
+Underneath the hood, the library uses [ulog](https://ulog.js.org/). To change the log level, add the parameter `log=[log-level]` eg, `http://localhost:3000/?log=debug`.
+
+For logging `>= log.INFO`, there is also a [frames per second stats](https://github.com/tibotiber/react-fps-stats).
+
+More documentation on the [ulog website](https://ulog.js.org/).
+
+### Run tests
+
+Run `npm test`
+
+Launches the test runner in the interactive watch mode.
+
+### Build the app
+
+Run `npm run build`
+
+Builds the app for production to the `build` folder.