About `anyadir_suscriptor_a_lista` and `eliminar_suscriptor_de_lista`... unless we're using this elsewere, what's the point of creating a method to call another method? `sendgrid.add_email` could have been called directly... 

```ruby
anyadir_suscriptor_a_lista(nombre_lista, datos_suscriptor)
```
```ruby
sendgrid.add_email(nombre_lista, datos_suscriptor)
```
Same readability and performance in both versions... we can save those "fat" methods