* Allow one to get a `Popularity` where `.rating` is always between 1 and 5
via `TagValue::toScaledPopularity()` (or a "raw" scale by specifying the
corresponding tag format)
* Allow one to assign a `Popularity` with `.scale = TagType::Unspecified`
and `.rating` between 1 and 5 (or a "raw" scale by specifying the
corresponding tag format). It will then be converted internally to
the required scale (whatever the tag format internally uses)
* Ensure all tag formats with popularity/rating field use
`TagValue::toScaledPopularity()` internally when a `Popularity`
object is assigned
* Ensure all tag formats with popularity/rating field store the rating as
popularity object to preserve the scaling information
* Keep passing raw strings around working
* `TagValue::toString()` still does *no* scaling
* `TagValue::toScaledPopularity()` does *no* scaling for text values
and instead just assigns the specified scale
* See https://github.com/Martchus/tagparser/issues/23
Martchus
c3c525c352