It's very easy to accidentally release libs with missing types

[mike-north]

When certain TS errors are encountered while compiling a module, the /dist/types/*.d.ts file may omit interfaces, or be missing entirely. Neither npm run-script problems or npm test ends up catching this, making it very easy to release broken library versions.

To reproduce:

1. Create a new library from the libkit blueprint
2. Put this at the top of /src/index.ts

type WithHello<T> = T & { hello: 'world' };

export interface Foo {
  name: string;
}
export interface Bar extends WithHello<Foo> {}

export const x: Bar = {
  hello: 'world',
  name: 'libkit'
};

3. Run npm run-script problems & npm run-script build (note it exits successfully)
4. Check the contents of /dist/types. It will be empty
5. Change /src/index.ts

- type WithHello<T> = T & { hello: 'world' };
+ export type WithHello<T> = T & { hello: 'world' };

6. Run npm run-script problems & npm run-script build (note it exits successfully)
7. Check the contents of /dist/types. It will contain the appropriate interfaces/types

This particular TS error is more likely to slip through -- it won't cause tests to fail. I suggest we either make npm run-script problems detect this kind of thing, or hard fail in the presence of any error that could result in incomplete output.