Progress: add more directory and file related functions, other changes

Progress: add more directory and file related functions, other changes

This was started with the intention of providing all of the *_at() functions.
However, the POSIX spec seems to fall short in many areas making this more difficult than this should be.
I partially rolled back some of the planned changes and this changeset is the result.

I have observed that the function return documentation needs to be updated, but this will be done at a later time.
There will need to be some intensive testing later on but for now I am committing and moving forward.