macro to declare all kind of operators for enums

[leissa]

enum class E {
    A = 1,
    B = 2,
    C = 4,
};

THORIN_ENUM_OPERATORS(E)
//...
auto x = E::A | E::B;
auto y = x ^ E::C;

Also switching to scoped enums at some spots like core::Mode, math::Mode, etc.