Prevent double buffering by exposing the BufRead bound

[sftse]

This is a bit of a nit, but interfaces that expose Read bounds should not do internal buffering, as this risks the caller accidentally passing a type that is already buffered, resulting in double buffering. Instead, by exposing the BufRead bound the caller is forced to buffer if he tries passing a type that only implements Read. Since the caller has better awareness of the code he is writing, he is much less likely to accidentally buffer a reader twice.