Core::spawn
* Add basic multicore fifo example * Add documentation for multicore * Send system_clock frequency to core1 over FIFO in example * Add Stack::new() to HAL. Use Stack::new() in example
Fixes: https://github.com/rp-rs/rp-hal/issues/218
mvp multicore implementation Co-authored-by: Jan Niehusmann <jan@gondor.com>