#### Summary

It would be nice to export a typeguard from Axios' index.d.ts.
This way, consumers trying to do error handling can check in a type-safe way if the error is an AxiosError, or some other kind of error.

It's easy enough to do this as a consumer, but it would be nicer if this was included in the actual Axios library.

test/typescript/axios.ts
AxiosResponse,
  AxiosError,
  AxiosInstance,
  AxiosAdapter,
  Cancel,
  CancelToken,
  CancelTokenSource,
  Canceler
} from '../../';
const config: AxiosRequestConfig = {
  url: '/user',
  method: 'get',
  baseURL: 'https://api.example.com/',
  transformRequest: (data: any) => '{"foo":"bar"}',
  transformResponse: [
    (data: any) => ({ baz: 'qux' })
  ],
  headers: { 'X-FOO': 'bar' },
  params: { id: 12345 },
  paramsSerializer: (params: any) => 'id=12345',
  data: { foo: 'bar' },
  timeout: 10000,
  withCredentials: true,
  auth: {
    username: 'janedoe',
    password: 's00pers3cret'
  },
  responseType: 'json',
  xsrfCookieName: 'XSRF-TOKEN',
  xsrfHeaderName: 'X-XSRF-TOKEN',