Intercept stdout so rogue `println`s still work correctly

[JakeWharton]

[JakeWharton]

I think we'll do this as part of raw mode, since that will screw up your trailing newlines on a println anyway (you need a full CRLF).

On JVM we capture stdout and replace with our own thing. Flip back on close.

On native POSIX I think we can do a freopen to a pipe that we also read. Not quite sure how to flip back.

On native Windows we can SetStdHandle to an anonymous pipe. Flip back on close.

[JakeWharton]

Probably blocked on doing this until we fix #508 since reads from these will need to flow into static logs.

[JakeWharton]

What happens when you write hello\nworld (note the lack of trailing newline)? Do we output "hello\n" and then just wait for a newline before writing "world\n" some frame later?