Add TypeScript type declaration

[johnnyoshika]

This is the TypeScript type declaration:

declare module 'exit-intent-quattro' {
  export interface Config {
    edges?: {
      top?: boolean;
      right?: boolean;
      bottom?: boolean;
      left?: boolean;
    };
    threshold?: number;
    maxDisplays?: number;
    eventThrottle?: number;
    onExitIntent: () => void;
  }

  export default function ExitIntent(options?: Config): () => void;
}

I wasn't able to configure rollup to convert this to an es module during build, so I had to exclude the type declaration from this project.