Add input/output redirection support

[TanmayPatil105]

Support for input/output/error redirection can be added. For example, if I want to execute cargo run -- < FILE or cargo run -- < DIRECTORY. We can have a redirect_input method as follows:

cmd.redirect_stdin(&path);

Similarly for flushing the stdout and stderr to a file. We can have redirect_stdout and redirect_stderr. I'm not sure if it's possible but I think it would be quite useful.

[epage]

Note that we have Command::pipe_stdin which sounds like your redirect_stdin.

Doing similar for stdout and stderr is a bit odd because we only return a std::process::Output. It doesn't quite fit for Assert to return it.