Feedback on implementation of decoding of chained streams

Hi all,

As some of you may know, the Ogg container is allowed to be 'chained',
meaning Ogg files or streams can simply be concatenated into a single
file or stream. This is something the vorbis and opus tools have
supported for some time, but FLAC hasn't.

Anyway, there are a few internet radio stations using chained Ogg FLAC
streams, and I was for a few years getting requests (and some
rudimentary implementations) to get this implemented. I've taken this
up the past few weeks and the result is quite a large change to the
current code base and some API changes.

Everything works, but as is with any change to the API, I don't know
whether it is convenient for API users other than the flac command
line tool. So, I'd like some feedback.

Proposal is here: https://github.com/xiph/flac/pull/735

Kind regards, Martijn van Beurden