Utility functions concerning the OCaml-runtime
last_accessed path returns the time path was last accessed.
For files, the access time is updated whenever the file is read or executed.
Note that some filesystems do not implement access time updates, or may allow
mounting with access time updates disabled.
last_modify path returns the time the file at path was last modified.
For files, the modify time is updated whenever path is written to, or if
its status attributes are updated.
last_changed path returns the time path last had its status changed.
This is not the same as last modified, as the last status change will also
be updated if path's ownership or permissions change.