There's a lot of variation in doc comments and internal code about
whether chmod/0o777-style permissions are called `mode` or `perm`. (For
example, mkdir and writeFile choose differently.)
Had proposed earlier to go consistently with `perm`, but on balance devs
prefer to go with `mode`.
There's a lot of variation in doc comments and internal code about
whether the first parameter to file system calls is `path` or `name` or
`filename`. For consistency, have made it always be `path`.
