Create a new directory with the specified path. If exclusive is true,
the returned Future will complete with an error if a directory already
exists with the specified path.
Retrieve an already existing directory entry. The returned future will
result in an error if a directory at path does not exist or if the item
at path is not a directory.
Create a new file with the specified path. If exclusive is true,
the returned Future will complete with an error if a file already
exists at the specified path.
Retrieve an already existing file entry. The returned future will
result in an error if a file at path does not exist or if the item at
path is not a file.