client: implement io.Reader
client: implement io.Reader

I'm thinking this code won't be used frequently since io.ReaderAt or
io.WriterTo is more likely, but I at least need some kind of Reader impl
and this should work.

Of course, at this point, I've not tested any of this.

couchbaselabs/cbfs,couchbaselabs/cbfs,couchbaselabs/cbfs