tools/test-itch41: Message type stats

Add message type stat printing to test-itc41 program. Example output:

[penberg@golgotha libtrading]$ ./tools/test-itch41 ../data/nasdaq/S123110-v41.txt.gz
 Message type stats for '../data/nasdaq/S123110-v41.txt.gz':

        46,825  Timestamp - Seconds
             6  System Event
         7,776  Stock Directory
         7,779  Stock Trading Action
             0  REG SHO Restriction
       318,355  Market Participant Position
    60,072,466  Add Order
     9,106,358  Add Order - MPID Attribution
     2,814,336  Order Executed
        47,097  Order Executed With Price
       501,104  Order Cancel
    66,998,982  Order Delete
     9,362,883  Order Replace
       271,518  Trade (non-cross)
        15,550  Cross Trade
             4  Broken Trade
     1,119,600  NOII

Signed-off-by: Pekka Enberg <penberg@kernel.org>