#### 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/specs/api.spec.js
expect(typeof axios.all).toEqual('function');
    expect(typeof axios.spread).toEqual('function');
  });
  it('should have factory method', function () {
    expect(typeof axios.create).toEqual('function');
  });
  it('should have Cancel, CancelToken, and isCancel properties', function () {
    expect(typeof axios.Cancel).toEqual('function');
    expect(typeof axios.CancelToken).toEqual('function');
    expect(typeof axios.isCancel).toEqual('function');
  });
});
describe('instance api', function () {
  var instance = axios.create();
  it('should have request methods', function () {
    expect(typeof instance.request).toEqual('function');
    expect(typeof instance.get).toEqual('function');
    expect(typeof instance.options).toEqual('function');
    expect(typeof instance.head).toEqual('function');
    expect(typeof instance.delete).toEqual('function');
    expect(typeof instance.post).toEqual('function');
    expect(typeof instance.put).toEqual('function');
    expect(typeof instance.patch).toEqual('function');
  });
  it('should have interceptors', function () {
    expect(typeof instance.interceptors.request).toEqual('object');
    expect(typeof instance.interceptors.response).toEqual('object');
  });
});