With this, `redoxfs --get-uuid <disk>` prints out the UUID of the
provided redoxfs disk image.

This is needed especially for aarch64 kernels where the UUID of the boot
disk needs to be passed to the kernel by the bootloader. With this
extension to the mount command, the kernel build glue can query the
prepared redoxfs image for it's UUID.

Cleanup to allow use of most functions when linking the library, including mounting and creating filesystems

This seems to be a warning with the latest Rust, and an error due to #![deny(warnings)]