* feat(output): Generate dot file and support multi outformat.(#441)

* [fix] forget to clean the dot generated file.

* [fix] indentation

* [fix] Review + add more cases in unittest

* [fix] Add dot in the test

`graphviz` only support string or byte-like objects as value in attributes. The example was passing `fontsize` as `int` that throws `TypeError`.

Just fixing the example

This allows you to have a consistent output filename, even if you decide
to tweak the diagram name.