0.8.3

Introduces Backend's models

This release introduces a new module, backends.models, which is intended to make easier to write a custom backend.

Highlighted changes:

- Introduces new module: backends.models
- Refactor some backends using the new module backends.models
- Add backends status to README
- Better and cleaner documentation
- Python 3's f-Strings for backends modules
- Upgraded dependency for requests package (fix vulnerability)
- Split into several files the sphinx's documentation
- Migrate reports from coverage to codecov
- Fix backend IRadioStore (ShoutCast Radio)
- Fix backend TEDStore
- Fix backend LolcatsStore
- Fix backend AppleTrailersStore
- Fix the parsing of the soap messages with encoding declared