Examplem macros:
```rust
/// Syntax helper for setting global variables of the form `Mutex<RefCell<Option>>>`.
/// eg in interrupt handlers. Ideal for non-copy-type variables that can't be initialized
/// immediatiately.
///
/// Example: `make_globals!(
///     (USB_SERIAL, SerialPort<UsbBusType>),
///     (DELAY, Delay),
/// )`
#[macro_export]
macro_rules! make_globals {
    ($(($NAME:ident, $type:ty)),+) => {
        $(
            static $NAME: Mutex<RefCell<Option<$type>>> = Mutex::new(RefCell::new(None));
        )+
    };
}
```