Creates a new `pub const &str` that is called `ENV_(string you put in)` and has the exact value of what you put in.

named_env_var_macro.rs

/// Creates a new `pub const &str` that is called `ENV_(string you put in)` and has the exact value of what you put in.
///
/// Example:
///
///     named_env_var!("FOO");
///     assert_eq!(ENV_FOO, "FOO");
///
macro_rules! named_env_var {
    ($name:expr) => {
        pub const concat!("ENV_", $name): &str = $name;
    };
}