Generate d.ts automatically

[mmktomato]

Problem

I have to edit dist/backlog.d.ts by myself if I change a type in src/. There's some problems:

• Risks of forgetting or making a mistake to edit dist/backlog.d.ts.
• Annoying.

Goal

No manually editing dist/backlog.d.ts.

Idea

npm run build-tsd creates declaration files in dist/src/*.d.ts. I want to use the files instead of dist/backlog.d.ts. Can "types": "dist/src/index.d.ts" in package.json do it?

[mmktomato]

Experiment in this branch.