NUMA memory info

[chabbimilind]

The Node structure does not include per NUMA node physical memory statistics.

type Node struct {
	ID     int                  `json:"id"`
	Cores  []*cpu.ProcessorCore `json:"cores"`
	Caches []*memory.Cache      `json:"caches"`
}

Can we add Memory []*memory.Info field to the struct and provide per-NUMA-node memory stats?

On Linux, /sys/devices/system/node/node*/meminfo file will offer the necessary data.
We need to augment pkg/memory/memory_linux.go with a function such as MemoryForNode() and call it from func topologyNodes in pkg/topology/topology_linux.go.

[ffromani]

I'd happy to work in this area in the coming days/weeks.

[ffromani]

begun working on a PR to fix this issue, but we're at the every early stages: #268