As a result, services don't always have to provide a `reqwest::Error`
but also return other errors. The error variant `Error::NotAuthorized`
in particular specifies that requests are not or no longer allowed and a
login should be (re)attempted. This way, services can indicate that it
is in this state and not have to provided a 403 status code
`reqwest::Error` to show this.
Add a depend on the `thiserror` crate for this.
Sometimes it can be that `today_eq` is reset when the day switches but
it has not been added to `total_eq` yet. The `total_eq` should always be
non-decreasing, so return the last known value until this is corrected
(this most suredly happens during the night).
Also, allow for `login` and `update` to mutate the state of the service
to be able to update things like the last known total produced energy
value.
Paul van Tilburg