Adding Crunch

Description: Fast arbitraty-precision integer arithmetic library. Used
for large-number calculations including finding large prime numbers,
performing modular exponentiation and other arithmetic operations.
Author: Nenad Vukicevic
License: MIT
Source: https://github.com/vukicevic/crunch/blob/master/crunch.js
Merge pull request #3328 from JGallardo/master

Adding Crunch