Provide typescript definitions

[ajmas]

It would be good to have some typescript definitions for this package. Right now i have needed to set "noImplicitAny": false in my `tsconfig.json' and also provide this hacky workaround, in my boot file (I am using Quasar on top of Vue):

declare module '@vue/runtime-core' {
  interface ComponentCustomProperties {
    $auth: any;
  }
}

[ajmas]

Looks like there are two pending PRs that address this in some way:

• Add typescript definitions & package.json config #196
• TS refactoring #228