Update Webpack config like scratch-storage

- Move build outputs into `dist/`
- Make build output file names more consistent
- Update `playground/index.html` for new output file name
- Explicitly specify target => Node output is much smaller
- Minor fixes / cleanup in `.gitignore` and `src/index*.js`

.gitignore

@@ -5,7 +5,13 @@
 /node_modules
 npm-*
 
+# Testing
+/.nyc_output
+/coverage
+
+# IDEA
+/.idea
+
 # Build
-/render*.js
-/dist.js
-/playground/render.js
+/dist
+/playground/scratch-render.js