Lightweight error-handling.

Provides Option<T>::oops(self, &str) -> Result<T>.

```rust use std::io::Result;

use oops::Opps;

fn third_element(slice: &[usize]) -> Result<&usize> { slice.iter().nth(3).oops("No third element") }

fn main() -> Result<()> { third_element(&[1, 2, 3]) } ```