Re-organize the repo

[stefano-garzarella]

@00xc originally started the work on #877

TSC asked to move only tools for now, but we should continue the discussion about other crates:

@00xc in the last TSC meeting we discussed a bit the repo reorganization, and we are not sure about lib/, we would like to discuss that a bit more (e.g lib/ vs topics vs user/kernel, etc.)

So our suggestion for now is to remove that changes from this PR and keep only the moves of tools, except for xbuild, which we consider to be more relevant to the build system of the entire project, so we thnk it is better that it lives in the root.

Originally posted by @stefano-garzarella in #877 (review)

[stefano-garzarella]

Perhaps instead of having lib, we should divide it by topics, so I would put packit in tools, virtio-drivers in drivers/, and so on.

Originally posted by @stefano-garzarella in #877 (comment)

[00xc]

Independently of the scheme, I'd say we could move the verify_* and verus_* crates to a verif/ path, since I don't think they would belong anywhere else.

[stefano-garzarella]

Independently of the scheme, I'd say we could move the verify_* and verus_* crates to a verif/ path, since I don't think they would belong anywhere else.

@00xc yeah, agree on that!

[00xc]

For the rest of crates, how about something less fine grained than my original proposal? e.g.

# Build infra
build/
	xbuild/
	configs/
	release/

# Libraries
crates/
	bootlib/
	cpuarch/
	elf/
	libaproxy/
	syscall/
	packit/
	virtio-drivers/
	test/

We leave Documentation, tools/ and user/, fuzz/, stage1 and kernel/ as they are.