Replace with or Wrap rbuf

[freb]

I found an interesting ring buffer lib. Originally, I was thinking I would use it to replace our own forked circbuf lib. However, rbuf has a Read method which makes it a reader. It also has some methods similar to this library. If it has what we need, we could replace this library with it entirely. If it doesn't this library should just become a light weight wrapper.

[freb]

I don't actually think that rbuf will offer us much by way of performance since it turns out the performance of unread isn't bad after wrapping the underlying reader in a buffio.Reader. I think the ping-pong buffers in rbuf mainly make a difference doing specific types of reads, but I could be wrong. Still worth looking into, but not urgent.