(1) std::vector< std::pair< T, usize > >
run_length_encoding<T, Iter>(Iter first, Iter last)
(2) std::vector< std::pair< T, usize > >
run_length_encoding<T>(const std::vector<T> &vs)
(3) std::vector< std::pair< char, usize > >
run_length_encoding<T>(const std::string &s)