Code generation from TS type aliases

TS exposes [custom transformers](https://github.com/Microsoft/TypeScript/issues/13764) through the public API, so it should be possible to create generates purely from a type alias. I've done something like before with [babel as Flow](https://github.com/unbounce/babel-plugin-transform-flow-to-gen).

```ts
import { fromType } from 'kitimat-type-to-gen';

const person = fromType();

// would expand to something like...

const kitimat = require('kitimat-jest');
const person = kitimat.object({
name: kitimat.string(),
age: kitimat.posInt(),
// ... etc
});