Remove "atomic operator" classes
Remove test, test_and_set, test_and_reset, test_and_complement global functions
Simplify atomic_t<> with constexpr if, remove some garbage
Redesign bs_t<> to use class, mark its methods constexpr
Implement atomic_bs_t<> for optimizations
Remove unused __bitwise_ops concept (should be in other header anyway)
Bitsets can now be tested via safe bool conversion