Add typescript types index.d.ts

Here's a head start:

```ts
import ejs from "ejs";
//@ts-ignore
import _ejsLint from "ejs-lint";

interface EjsLintResponse {
  annotated: string;
  column: number;
  line: number;
  message: string;
}

type EjsLintFunc = (
  template: string,
  data?: ejs.Data | undefined
) => EjsLintResponse;

const ejsLint = _ejsLint as EjsLintFunc
```