code: function readPartial(multibuffer) {
    var dataLength = vdecode(multibuffer)
    var read = vdecode.bytes
    if (multibuffer.length < read + dataLength) return [null, multibuffer]
    var first = multibuffer.slice(read, read + dataLength)
    var rest = multibuffer.slice(read + dataLength)
    if (rest.length === 0) rest = null
    return [first, rest]
  }
docs: Fetch the first encoded buffer from a multibuffer, and the rest of the multibuffer.
  @param  {Buffer} multibuffer An encoded multibuffer.
  @return {Array}            [Buffer, Buffer] where the first buffer is the first encoded buffer, and the second is the rest of the multibuffer.