TS BUG: need declaration: false to build correctly

If we set declaration: true, then typescript (specifically rpt2,
Rollup's TS plugin) fails with a cryptic path error. This is
filed under microsoft/TypeScript#25047.

Curiously, this does not happen on master, and I have vaguely
traced it back to unionize and the fact that it does fancy type
exports, which we partially re-export here. We would have to
manually emit a declaration file, which is not hard tbh, but a bit
annoying. Even funnier, webpack has no issue building in storybook,
but that might be because it does not emit declarations anyway.

Steps:
- Get declaration file from master, add to repository, and copy to
dist/ upon build;
- See if massaging our exports fixes it;
- Wait for TS :/

Author: fpapado

tsconfig.json

@@ -2,7 +2,7 @@
   "compilerOptions": {
     "module": "es2015",
     "target": "es5",
-    "declaration": true,
+    "declaration": false,
     "sourceMap": true,
     "jsx": "react",
     "allowJs": false,