Memory

Note: This only apples to the C++ target

I've done some testing with the jemalloc memory allocator. All standard tests pass, and I've observed some performance improvements – one case showed a 4x runtime speed increase over using the standard system allocator, and that was just for a single-threaded case (more testing and benchmarking would be good). Simply linking with the library via LDFLAGS was all that was needed to use it.