Program emulates C's perror.
```rust use program::perror; use std::io::{self};
fn printmsg(: &str) -> io::Result<()> { Err(io::Error::new( io::ErrorKind::Other, "something went wrong!", )) }
fn main() {
if let Err(e) = print_msg("Hello, world!") {
perror(e);
}
}
$ cargo run
Compiling example v0.1.0 (/root/example)
Finished dev [unoptimized + debuginfo] target(s) in 0.34s
Running target/debug/example
example: something went wrong!
```