Change data source to apidatos.ree.es

🔥 BREAKING-CHANGE: this release removes support for the old PVPC tariffs (prices < 2021-06-01), and the extra methods to use this library as a dataloader (.download_prices_for_range(...)), leaving only the code to support the HA Core integration.

Motivated by recent successful attempts to kick us out from api.esios.ree.es, we are changing the data source to another server, at apidatos.ree.es.

👏 As suggested by @lazynoda in this comment, REE has another public and documented API (REData API) with the same information as the current one, available without authentication 👌, so it may deserve a chance 🤞.

This release implements the new data-source, but also maintains the legacy one.

• Initial configuration is set with a new data_source parameter, with the new source as default.
• If a 403 status-code is received, the data source is switched (new to legacy / legacy to new), no retry is done (and the User-Agent loop trick is only used for the legacy data source)

Changes in #39