Function pspawn

pub fn pspawn(
    name: Option<&str>,
    path: &str,
    argv: Vec<&str>,
    flags: SpawnFlags,
    stdin: Option<usize>,
    stdout: Option<usize>,
    stderr: Option<usize>,
) -> Result<usize, ErrorStatus>

same as unsafe_pspawn but safe because it makes it clear that argv is consumed`