vfs abstractions and tarfs

[ojeda]

Nits in commit messages:

• "This is a modifid version" typo
• "This allows file system" -> "This allows file systems" (x2)
• "associated to inodes": "to" or "with"?
• "xattr_handler" -> "xattr_handler"
• "for simple structs that whose fields" -> "for simple structs whose fields"
• "the rust version" -> "the Rust version"
• "by rust file systems" -> "by Rust file systems"