#### 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
.then(handleStringResponse)
  .catch(handleError);
axios.post<User, string>('/user', { foo: 'bar' })
  .then(handleStringResponse)
  .catch(handleError);
axios.post<User, string>('/user', { foo: 'bar' }, { headers: { 'X-FOO': 'bar' } })
  .then(handleStringResponse)
  .catch(handleError);
axios.put<User, string>('/user', { foo: 'bar' })
  .then(handleStringResponse)
  .catch(handleError);
axios.patch<User, string>('/user', { foo: 'bar' })
  .then(handleStringResponse)
  .catch(handleError);
axios.request<User, string>({
  method: 'get',
  url: '/user?id=12345'
})
  .then(handleStringResponse)
  .catch(handleError);
const instance1: AxiosInstance = axios.create();
const instance2: AxiosInstance = axios.create(config);
instance1(config)
  .then(handleResponse)
  .catch(handleError);
instance1.request(config)
  .then(handleResponse)
  .catch(handleError);
instance1.get('/user?id=12345')
  .then(handleResponse)