Enable generation of TypeScript typings (#32)

tsconfig.package.json

@@ -2,7 +2,7 @@
   "compilerOptions": {
     "forceConsistentCasingInFileNames": true,
     "sourceMap": true,
-    "declaration": false,
+    "declaration": true,
     "noImplicitReturns": true,
     "noUnusedLocals": true,
     "noUnusedParameters": true,