`-d` and `--directory` flag not correct against `ls`

[roberthawdon]

In ls, the -d flag displays only the current directory. In show, this flag lists all directories in the current path.

This should be changed so -d and --directory shows just ., and a new, show exclusive, argument should be added to list all directories.

[roberthawdon]

Added new show only option for listing only directories to make way for this.

[roberthawdon]

Added to v0.10.0-dev branch

[roberthawdon]

Documentation needs amending #161