The previous method of taking the channel could cause deadlock, we now
use semaphore to signal if the channel is available instead of busy
polling the mutex.
SZL no longer do self-extraction for runtime binary, it would boot from
SD/ethernet depending on the boot mode settings.
This allows a larger runtime binary, so we can optimize for speed in the
runtime firmware for better performance, and allow more features to be
added later.
* based on https://github.com/jethrogb/rust-core_io but could not get the packaging scripts to work
and the repos is unmaintained anyway, so just copied the result
* more features and more up-to-date
* compatible with the fatfs crate
