Switch example tools to use VBR and 960 sample frames by default on the basis...

Switch example tools to use VBR and 960 sample frames by default on the basis that if the user doesn't have any particular requirements that they probably want this.

Minor change in the VBR behavior to hot-start with some internal state
parameters which were observed to be quite consistent across bitrates,
framesizes, and content. This also prevents it from completely burning
the reserve capacity on the first frame if its a short.

Also switch some maximum frame sizes to match the OPUS draft maximums.