Add support for different styles (--style=plain option) about graph-composer

[Danack]

Hi,

Thought I'd stick this in here rather than create new issue - one thing that would be awesome to have is the ability to set which main orientation is used.

Currently the root project is at the top, and then the dependencies get listed underneath. For projects that have many dependencies this produces a graph that is very wide. This isn't helped by the fact that English text is written horizontally.

It would be nice to be able to set the flow to be vertical, with the root dependency on the left and then the dependencies listed to the right, which appears to be achievable with setting rankdir="LR" rather than the default value it has of 'TB'

http://www.graphviz.org/doc/info/attrs.html#d:rankdir

[clue]

As much as I'd love to work on this myself, there are currently no immediate plans to build this from my end (no demand at the moment and more important outstanding issues currently). If you need this for a commercial project and you want to help sponsor this feature, feel free to reach out and I'm happy to take a look.

---

@Danack Horizontal orientation makes a lot of sense! See #36 as a follow-up for this.