Expose types correctly and add support for generic annotations

[joelpoloney]

Fixed 2 things:

1. The TypeScript definitions were not being exposed correctly, the change to package.json fixes that. I followed the instructions at https://www.typescriptlang.org/docs/handbook/declaration-files/publishing.html.
2. Expose the key property that is provided to renderHighlight -- this definition was out of date.

Added new:

1. Support for generic IAnnotation objects so you can use your own version of the Annotation object and include your own data outside of just text and an id. You use it like this:

   import { IAnnotation } from 'react-image-annotation'
   
   export interface MyAnnotation extends Omit<IAnnotation, 'data'> {
     data: {
       id?: string
       updatedAt: Date
       type: string
       userVisibleName: string
       metadata: Record<string, unknown>
     }
   }