feat: support to FileInfo.Sys() (#19)

Co-authored-by: Liam Galvin <liamgalvin@protonmail.com>

feat: Add SetModified (#17)

fix: allow filenames prefixed with a dot (#16)

fix: close dangling lazy written files (#15)

feat: Add RemoveAll functionality (#14)

Signed-off-by: Owen Rumney <owen@owenrumney.co.uk>

feat: Add remove functionality (#13)

* feat: Add remove functionality

Signed-off-by: Owen Rumney <owen@owenrumney.co.uk>

* feat: Add RemoveAll functionality

Signed-off-by: Owen Rumney <owen@owenrumney.co.uk>

feat: Add ExtendFS to take one FS and make a new one from it (#12)

* feat: Add ExtendFS to take one FS and make a new one from it

This is particularly dandy in situations when you have something that
implements fs.FS but you can't write to it and you want a memoryfs.FS to
work with and add stuff too.

feat: better cross-platform support (#11)

fix: Fix Windows support (#10)

docs: Fix typos (#9)