- Name std::hash only once the object type has emplace_new_key: VS 2015
static-asserts on std::hash of a type without one (alt_string) instead of
reporting a substitution failure (C2338).
- Replace the std::copy calls on frames by loops: VS 2015 reports raw
pointers handed to std::copy as C4996, an error under /WX.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>