Improvements around for the PosixPermissions api about fs2 HOT 3 CLOSED

Adding some builder methods to PosixPermissions sounds good to me. Both add and remove maybe?

I could also see something like:

• p.modify("+x")
• PosixPermissionChange.fromString("+x").traverse(p.modify)
• p | PosixPermissions.fromString("x--x--x--").get
• p + PosixPermissions.fromString("x--x--x--").get and p - PosixPermissions.fromString("x--x--x--").get

from fs2.

Fixed by #3396

from fs2.

I just spent some time working on the additional changes we talked about. and TIL, that chmod supports a lot more than I had anticipated, see the docs.

For example one can do: u=g to set the [u]sers permissions to whatever the [g]roup permissions are. You can also do +x,+w.

Do we want to match what chmod can accepts, or allowing a subset of that would be reasonable? eg:

1. "+x" add executable bit to all
2. "u-r" removes the read bit for users
3. "g=rw" sets the group permission as "rw-" (remove executable if it's there)

from fs2.