C++20 removed std::result_of, and it's pretty important for Hana to
support C++20. We could have conditionally supported std::result_of,
however I feel like it's reasonable to require users to move away from
the trait entirely. Staying on deprecated/removing features is not a
healthy thing to do anyway.
Fixes#462
- Split type class instances into separate files
- Instances provided automatically by a type class are actually MCDs
- Test each instance in a single file, not one file per method
- Refactor the operator system to fix the ADL-related bug.
