Basically mirroring the changes done for Corrade::Compare::*File*,
including storing the filenames as string views to avoid unnecessary
copies (and then paying extra attention to not pass temporaries to them
in its own tests).
Pros:
* faster compile times (#include <tuple> is 13k lines, ugh)
* ability to have NoInit and ZeroInit constructors
* ability to do fuzzy compare
* named members, so we don't have to use mutable std::tie()
Cons:
* ... none?
The old Color[34]::Hsv is still a tuple and the new ColorHsv is
convertible to/from it (and even std::tie() works). These are all
deprecated (along with the <tuple> include).