Adding memmem() to QB64PE

[Petr]

Over my head, but love the passion!

@a740g @offbyone @rhosigma @smcneill are needed here.

Yeah, can we get a laymen's description of this, for us mere mortals? 

If that's what I'm thinking, it should search for a larger block of bytes inside the memory block. Something like Instr or _Intsrrev but not for a string, but in the _MEM array. I would solve it by loading the block as a string and then using Instr or _Instrrev, but I don't really know if these functions can return a value of type _Integer64.

But it's also possible that it's something completely different.