Closing Stdio Pipes

[Aidan63]

Closing stdio pipes isn't something you really want to do and has inconsistent behaviour on libuv.

libuv/libuv#2962

So, what should we do if the user calls close on one of the stdio streams in Process.current. Right now I just invoke the success callback and do nothing behind the scenese. Given that closing stdio is dangerous, and I'm not sure what what the use case of this is on the haxe side either, maybe close shouldn't be exposed here?