Suggestion: FAT filesystem impl as its own crate.

[nihalpasham]

Firstly, thank you for this repo. It saved me a ton of time. 👍🏾 (I'm posting this as an issue as I couldn't find a discussions tab)

I'd like to make a suggestion - can we split the FAT filesystem impl into its own crate as the current implementation is pretty modular and it doesn't take a lot to turn it into a standalone crate. I wrote a bare-metal EMMC driver for the raspberry-pi 4 using embedded-sdmmc-rs (sans the SdMmcSpi controller).

• Reason: rpi4 now has an emmc2-controller with dedicated pins connecting it to the on-board microSD slot and this slot isn't accessible via SPI.

I think a standalone no_std fat-fs crate would be easier to work with when adding fat-support to block devices driven by other (non-spi) controllers.

[MathiasKoch]

Just in case it was somehow missed, https://github.com/rafalh/rust-fatfs/ is no_std compatible and could perhaps be used eventually?

[nihalpasham]

Good to know, thank you. This is what I was looking for.