Large-file processing example for DOU BigData discussion thread.
Produces CRC16 (well soft of) value histogram for the input file.

Usage:
	mrcrc nproc input output

nproc is the number of processes to run in parallel.
output is just 0x10000 longs, the aggregate counters for each possible
CRC value.

Both input and (less importantly) output and mmaped whole regardless
of their size, taking advantage of virtual memory and long 64-bit pointers
common nowadays.

CRC code from
http://stackoverflow.com/questions/10564491/function-to-calculate-a-crc16
May or may not be correct, that's not really important as long as it provides
some CPU load and reasonably scattered output values.