Copy returns a copy of a `*big.Int`.

Div devides a by b and returns a new `*big.Int`.

EncodeToString uses [0-9a-zA-Z] for base62.

Equal checks if a == b.

IntToHex converts a `*big.Int` to a hex string.

Mod performs `a mod n`.

ModInt64 returns an int64 mod.

MustEncodeToString uses [0-9a-zA-Z] for base62.

NewIntHex converts a hex string to a `*big.Int`.

NewIntString creates a new `*big.Int` from an uint64.

NewIntUint64 creates a new `*big.Int` from an uint64.

Pow is the power function for big ints.