Add type checking and full build creation

This uses Closure Compiler to create a full build and run type checks.
Currently type errors are reported as warnings and the build is created
with SIMPLE optimizations until we have transitioned all types to path
types.

package.json

@@ -11,10 +11,11 @@
   "scripts": {
     "lint": "eslint tasks test src examples transforms",
     "pretest": "npm run lint",
-    "test": "npm run karma -- --single-run",
+    "test": "npm run karma -- --single-run && npm run build-typecheck",
     "karma": "karma start test/karma.config.js",
     "serve-examples": "mkdir -p build/examples && webpack --config examples/webpack/config.js --watch & serve build/examples",
-    "build-examples": "webpack --config examples/webpack/config.js --env=prod"
+    "build-examples": "webpack --config examples/webpack/config.js --env=prod",
+    "build-typecheck": "node tasks/generate-index.js && node tasks/build-typecheck.js"
   },
   "main": "src/ol/index.js",
   "repository": {
@@ -46,6 +47,7 @@
     "front-matter": "^2.1.2",
     "fs-extra": "5.0.0",
     "glob": "7.1.1",
+    "google-closure-compiler": "^20180101.0.0",
     "handlebars": "4.0.11",
     "html-webpack-plugin": "^2.30.1",
     "istanbul": "0.4.5",