[2018-06 CWG Motion 6] P0732R2 Class types in non-type template parameters

[jensmaurer]

P0732R2

[jensmaurer]

Asked @zygoloid whether he wants cross-reference changes / amendments as a fixup or as a separate repair commit.

[jensmaurer]

Got the answer, made the cross-references fixes "Fixup"s.

[jensmaurer]

The feature-test macro __cpp_nontype_template_parameter_class is added in #2200.