Reuse frameio infra for non-frame io

[iboB]

I did think of this while writing frameio, but now when working on acord, it's becoming increasingly obvious that reusing at the least of all channels, would be a good idea when moving data between WebSocket buffers and frames.

Templates are the obvious answer, but we can't make use of virtual functions in such a case as the vtables and type info would be all broken and the address sanitizer will go crazy... well we could, but we would have to forget about asan, which is a bad idea.

I'll have to think of something here...

[iboB]

The alternative here is to make ac::Frame so lightweight, that this doesn't matter. Then we could convert frames at io level without burdening the io execution too much.

Let's see where #227 takes us, and then we'll reprioritize this.

Meanwhile we'll do the "bad" thing and burden io