receipt. The encode algorithm looks like this:

	var u uint
	if i < 0 {
		u = (^uint(i) << 1) | 1 // complement i, bit 0 is 1
	} else {
		u = (uint(i) << 1) // do not complement i, bit 0 is 0
	}
	encodeUnsigned(u)

The low bit is therefore analogous to a sign bit, but making it the complement bit
instead guarantees that the largest negative integer is not a special case. For
example, -129=^128=(^256>>1) encodes as (FE 01 01).