Auto tuning combined bandwidth

The "PcieBandwidthBenchmarker.h" header includes PcieBandwidthBenchmarker class that benchmarks each physical card in system and finds their relative multiplier constants to maximize combined bandwidth for virtual array usage.

Usage:

// user allows it to use 128MB per card during benchmark
PcieBandwidthBenchmarker bench(128);

// user picks minimum allowed data channel(virtual gpu) per physical gpu
// example: 2 here
std::vector<int> multipliers = bench.bestBandwidth(2);

Output array on development machine becomes {3,4,2} because slowest connection is on 3rd pcie bridge. Rest are scaled with their own data copying performances.

std::vector<int> multipliers = bench.bestBandwidth(10); // multipliers = { 15,20,10}

Then it can be directly sent to constructor of VirtualMultiArray like this:

VirtualMultiArray<Obj> data(..,..,..,..,bench.bestBandwidth(2));

The data array uses that specified ratios of bandwidths which maps well to physical card communication performance under high-enough concurrent accesses to elements.