feat(volume): add caseSensitive option

[ajafff]

Defaults to 'true'. If 'false', handle file names case insensitive.
Preserve original file names.

Fixes: #533

[G-Rath]

I'll review this properly when I have a chance, but for now: I think I'd prefer this option to be ignoreCase with a default of false rather than have an option with a default of true as that tends to be easier to reason mentally.

[ajafff]

@G-Rath that makes sense. I'll update the PR accordingly.

I noticed that the sorting of readdir(Sync) should also respect case sensitivity. I'm currently working on that.

I should probably also update the docs.

[tstordyallison]

+1 for this. I'm playing around with using memfs in conjunction with some libraries that are assuming case-insensitivity on Windows platforms, which isn't the case when I'm using memfs! This would be an ideal fix.

[jburrow]

+1 Just hit the same issue with memfs on windows

[G-Rath]

Closing due to age - feel free to rebase this PR or open a new one if someone wants to pick it back up