feat: partial relative paths support

[Mopsgamer]

Warning

There was also a useless line nearby. It might be worth submitting it independently of this PR.

Refs #23

Partial support and not fully tested. Can this be merged as is, or should contributors finalize it?

Features

• New cwd property (getter + setter) is available for Volume and Superblock instances.

[Mopsgamer]

Sorry, I missed the merge conflicts. It was quite difficult to sort through the new changes. I noticed there are two options involving cwd, but it seems this PR needs another one.

The current interface looks like this:
memfs(json, cwd1, { process: {cwd2()}})

Right now, cwd2 acts as the mount point. From what I understand, cwd1 serves as the mount for cwd2, which seems a bit counterintuitive.

We should either add a new cwd3 option or redefine how cwd1 behaves.

cwd3 would set the current directory for resolving relative file paths within the methods.