Btrfs support?

[Conan-Kudo]

LittleKernel has FAT16/FAT32 and ext2 support (with ext4 support being added in #303). It would be great if there was also Btrfs support, too. There is an MIT-licensed read-only Btrfs implementation that could be used as the starting point in the form of btrfs-fuse by @adam900710.

[travisg]

It would be kinda fun, though that's a giant pile of code if nothing else. But there's a block io layer that folks can implement it against if they'd like!