pub fn prefixed<'a, C>(prefix: C) -> Prefixed<'a>
where
    C: Into<Cow<'a, str>>,
{
    Prefixed(prefix.into())
}
Produces a instance of `Prefixed` for prefixing env variable names

# Example

```no_run
use serde::Deserialize;

#[derive(Deserialize, Debug)]
struct Config {
foo: u16,
bar: bool,
baz: String,
boom: Option<u64>,
}

// all env variables will be expected to be prefixed with APP_
// i.e. APP_FOO, APP_BAR, etc
match envy::prefixed("APP_").from_env::<Config>() {
Ok(config) => println!("{:#?}", config),
Err(error) => eprintln!("{:#?}", error),
}
```
src/lib.rs