Feature request: option to change orientation when generate dotcode

[lennonwoo]

Sometimes, the left to right type orientation will cause the final dot graph too wide, and we may need the top to bottom orientation.
And currently, the codebase hard code the orientation of dotcode to 'LR' in this line.
Can we provide a check_box to enable 'BT' orientation?

[dirk-thomas]

Please consider to provide a pull request to implement this feature idea.