Add support for the -y flag

[AviSarmani]

Hi,
I need to add a functionality to use the "-y" flag which inverts the axis as documented here:
https://graphviz.org/doc/info/command.html#-y

I added the command to the "cmd" clause while debugging and looks like it works.

If I want to create a PR for it, do we want to go along the design of:
#131
which means adding another optional parameter?

Thanks in advance.

[xflr6]

Thanks. Can you maybe provide more detail about the use case, e.g. an example (IIUC this flag is only relevant for rendering into plain-text formats: I am wondering what the remainder of the pipeline looks like or what typical use cases for these formats are)?

+1, the first thing that comes to mind would be another optional parameter.

[AviSarmani]

Hi,
Our use case is that the graph was being rendered on the FE via viz.js but they were getting memory dumps with big graphs so we're transferring the graphviz part to the BE.
The specific call that they were making was:
this.viz.renderString(dot, { engine: 'dot', format: 'json', yInvert: true })
so I needed to add the corresponding -y flag on our BE call as well.

I've forked the project, added the flag and updated the existing tests to run correctly.
The fork works on our system correctly as it produces the same result without memory exhaustion.

This is the fork:
master...Datricks:add_axis_invert_support

I would love to open a PR but I haven't added unit testing on the new feature yet.
Do we have a guide or can I have some guidance on how(and where) to add the necessary tests?