u/vector: Add generic wrapper for std::vector

This MR is more of a RFC, I don't really need the dynamic array functionality at the moment in C.

Monado needs to deal with the containers for different underlying types, and for this there is usually duplicated code, like for example in m_filter_fifo, m_filter_one_euro, or the fact that there is only a hashmap for ints.

I was thinking maybe we could use macros like these to expose templated interfaces to C and thus added this small example to expose a subset of std::vector to C.