Add benchmark script to evaluate multi-threading speedup of coinciden…

[gertvanhoey]

Example output:

==================================================
  Threads   Wall time (s)   Speedup   Efficiency
--------------------------------------------------
        1          115.08      1.00x       100.0%
        2           59.14      1.95x        97.3%
        3           40.85      2.82x        93.9%
        4           31.88      3.61x        90.3%
        5           26.44      4.35x        87.0%
        6           22.40      5.14x        85.6%
        7           19.75      5.83x        83.3%
        8           19.42      5.93x        74.1%
        9           21.81      5.28x        58.6%
       10           21.15      5.44x        54.4%
==================================================

  Suggested optimum: 8 thread(s)  (last point where efficiency >= 70 %)