inverted flat layout

[solidiquis]

Closes #181

Added iflat to the layout enumerated argument:

-y, --layout <LAYOUT>
        Which kind of layout to use when rendering the output
        
        [default: regular]

        Possible values:
        - regular:  Outputs the tree with the root node at the bottom of the output
        - inverted: Outputs the tree with the root node at the top of the output
        - flat:     Outputs a flat layout using paths rather than an ASCII tree
        - iflat:    Outputs an inverted flat layout with the root at the top of the output