C++17: take advantage of overaligned operator new and aligned_alloc

[olupton]

In #834 we will increase the minimum C++ standard to C++17.

This should allow TODO items like

CoreNeuron/coreneuron/utils/memory.cpp

Lines 39 to 40 in 0574812

	// Allocate using standard operator new.
	// When we have C++17 support then propagate `alignment` here.

to be addressed. This should be helpful (also in NEURON) for structures that should be allocated overaligned (e.g. for SSE/AVX).

An initial attempt at addressing this was introduced in #834, but then removed again. Check the intermediate versions of that PR.

We can also use std::aligned_alloc instead of posix_memalign, and so on.