The previous configuration mixed Webpack output with static content in
order to create the playground. This change moves that static content
from `/playground/` into `/src/playground/` and adds a Webpack rule to
copy it into the playground as part of the build.
On the surface this might seem unnecessary, but it provides at least two
benefits:
- It's no longer possible to accidentally load stale build output
through `webpack-dev-server` in the event of a misconfiguration. This
was very easy in the previous configuration, and might in fact be the
only way that `webpack-dev-server` ever worked for this repository.
- It's simpler to ensure that various rules apply to the hand-authored
content and not build outputs. This includes lint rules, `.gitignore`,
IDE symbol search paths, etc.
* `module.loaders` -> `module.rules`
* loaders need `-loader` suffix
* `json-loader` is enabled by default
* `UglifyJsPlugin`'s `compress.warning` setting is false by default
* Move Node output: /dist.js => /dist/node/scratch-vm.js
* Move web output: /vm{.js,.min.js} => /dist/web/scratch-vm{.js,.min.js}
* Update build output references in package.json and the playground's index.html
* Move the VirtualMachine class out of index.js into its own file, referenced by index.js. The VirtualMachine class is otherwise unchanged.
* Add .gitattributes rules for new file types which were added to this repository without specifying their text/binary attributes
* Turn on source maps in webpack and add corresponding .gitignore rule