Matrix multiplication. More work per thread v.3 benchmark

WebGL2-compute based NxN matrix multiplication C = A x B
Shader v.3 benchmark.
Fixed random A, B 4096x4096 buffers are used for calculations,
therefore You can set new N value (up to N=4096, multiple of TS).
TS - tile sizes (local_size_x,y). it - number of iterations.
FLOPS = 2 N^{3}it / time.
Random C_{GPU} and C_{GPU} - C_{CPU} are shown.