Arbitrary-precision bigints

[stephentyrone]

Add a flexibly-sized bigint type that grows as required, conforming to BinaryInteger.

[rothomp3]

So I have a pretty good implementation of this already, would I need to propose it as a new module or does this issue mean it's gone through that part of the process?

[stephentyrone]

I think you can skip step 1, but otherwise that's the right process to follow.