namespace 'detail' now.

so far).

This reverts commit e5b5201c02.

Ref. #72

noexcept-value is missing in the document it is implemented as for
std::swap(). Fixes #73.

Fixes #71, fixes #67, fixes #66, fixes #63, fixes #58, fixes #51,
fixes #65.

the custom one.

on Travis CI (workaround for #72).

temporarily by old-style casts, as there were type issues.

ambiguous otherwise.

drop-in replacement with a future library implementation (#59).