Use DEC64 instead of Number

[wolfgang42]

Per the spec:

Numbers in Rockstar are stored using the DEC64 numeric type.

Presumably I'll need some sort of library for this. Stress-tests would also be nice, so once this is implemented we can brag about how much better than other implementations we are :)

[dylanrenwick]

I did some brief research and couldn't find any DEC64 libraries for Node.js, so it might need to be implemented from scratch in rockstar.js

I'll do some playing around tonight and see if I can find a solution without re-inventing "the wheel" (read: number types in js)

[aDotInTheVoid]

This Commit changed the number format to IEEE 754 double percision, so you could update your spec to solve this