please publish library with flow types

This is a:

- [ ] Bug Report
- [X] Feature Request
- [ ] Question
- [ ] Other

Which concerns:

- [X] flow-runtime
- [ ] babel-plugin-flow-runtime
- [ ] flow-runtime-validators
- [ ] flow-runtime-mobx
- [ ] flow-config-parser
- [ ] The documentation website

---

### What is the current behaviour?

`flow-typed install` places the following in `flow-typed/npm/flow-runtime_vx.x.x.js`:

~~~
declare module 'flow-runtime' {
declare module.exports: any;
}
~~~

This means that all usage of Type and its methods result in `any`.

---

### What is the expected behaviour?

Just export `.js.flow` in the distribution in addition to the `.js`. I have dabbled a bit with rollup but couldn’t figure out how to make that happen.

---

### Which package versions are you using?

flow-runtime 0.11.1

Start by inspecting the Rollup and package distribution configuration for flow-runtime. Check how the published package is assembled and how flow-typed install currently sees its declarations. Done means the distribution includes a .js.flow file alongside the .js file so Flow consumers receive typed exports.

Written by the indexing model from the issue text.