CAEA support

[erebodino]

Are CAEA operations supported? I'm not seen methods for request CAEA, see expiration dates or inform about receipts created with CAEA, but in Point of Sales the field Issuance type force you to choose between CAE or CAEA so I'm a little bit confused

[WhyNotHugo]

CAEA is not implemented. The field Issuance type has all the valid types because otherwise we wouldn't be able to implement TaxPayer.fetch_points_of_sales.

Patches to implement CAEA support are welcome.

The first thing needed is a model representing the CAEA, with all the fields that are returned when requesting it.

[WhyNotHugo]

Related: #164

[WhyNotHugo]

Note for implementors: ReceiptQrCode currently hardcodes "tipoCodAut": "E".