#2 Finish x86 assembly bigint

[Todd Bandrowsky]

The existing big int is a wrapper around the gnu bignum, which is pretty slow. It's slow partially because it is a genuinely big number, allowing for thousands or millions of digits. Can we just have a big int x86-64 assembly that does digits up a fixed number in the range we're interested in factoring. Certainly anything more than 2048 bits would be fanciful at this point.