Crate smallbigint

A wrapper around num_bigint::BigUint and num_bigint::BigInt that stays out of the heap for small values.

In the current implementation, we go to the heap for anything that doesn't fit in 32 bits.

This crate already has a lot of relevant methods, but it is not really complete yet. Patches are welcome!

Care has usually been taken to avoid allocation in the methods here, but not in all cases.

To do, and important:

• Implement std::fmt::{Binary, LowerHex, Octal, UpperHex} (easy?)
• Implement num_bigint::{ToBigInt, ToBigUint}
• Unit tests. Currently there are none, although the code is sufficiently simple that there is almost no place where bugs could hide.
• Make this compile against rust stable.

Other traits and methods still to be implemented:

• Bit operations
• num_traits::ops::checked traits
• num_traits::Num (easy?)
• num_traits::One (easy?)
• num_traits::Signed
• num_traits::Unsigned
• num_integer::Integer
• num_integer::Roots
• std::iter::Product
• std::iter::Sum
• Other methods implemented directly on BigInt, BigUint

Not done and seems hard:

• num_traits::pow::Pow

Structs

Int
IntIsNegativeError
Uint