npm package pragma?

It might be useful for a module to be able to specify that it's available as an npm package. Perhaps this could be some dnt specific pragma that lives in the file being imported that says the npm package name.

So, for example, say in `https://deno.land/x/code_block_writer@12.0.0/mod.ts`:

```ts
// dnt-npm-package: code-block-writer

export default class Writer {
}
```

Then:

```ts
import CodeBlockWriter from "https://deno.land/x/code_block_writer@12.0.0/mod.ts";
```

Would go to:

```ts
import CodeBlockWriter from "code-block-writer";
```

With a dependency of `^12.0.0`.