* add missing headers: ‹bit›, ‹map›, ‹queue› and ‹set›
* name the namespaces
* math
* introduce ‹MODULO› for big numbers in problems
* input
* implement ‹load_vector›
* output
* implement ‹operator<<› for ‹std::pair›
* implement ‹yesno› as shortcut for YES/NO answers
* implement ‹LOOP(n)› for quick range-like for-loops
* make ‹N› test cases the default
Signed-off-by: Matej Focko <me@mfocko.xyz>