fix(shuffle): malloc array_size try-retry

[tmkontra]

Changes:

• adds validate_array_size method
  • reduce by configurable step_size (set to 5%)
  • avoid later segmentation fault

Purpose: During development of a Cython wrapper for this library, I noticed segmentation faults when requesting too much memory via the -memory on the shuffle binary.

After much debugging to find the root cause, this commit had me implement a "self-healing" array_size. More advanced users may easily overcome this (by adjusting their -memory arg), but I recognize a strong segment of scientific users who may not be able to debug such an error.

I hope this is found useful. Please let me know if this is something you would consider merging, or what changes should be made (I'm rather new to C, so any feedback is appreciated). Cheers!