`copyEscapable` is a copy/paste of io.Copy with some added handling for
checking for the attach escape sequence.
This removes the copy/paste and uses `io.Copy` directly. To be able to
do this, it now implements an `io.Reader` which proxies to the main
reader but looks for the escape sequence.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
This cleans up attach a little bit, and moves it out of the container
package.
Really `AttachStream` is a method on `*stream.Config`, so moved if from
a package level function to one bound to `Config`.
In addition, uses a config struct rather than passing around tons and
tons of arguments.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
