Pass "args" via .json file rather than arguments to rust program

[drojf]

I wanted an easier way to pass data between the python and rust program (instead of the command line), so I made the python script write to a temporary .json file which the Rust file reads.

I guess it could just pass it via stdin instead, but I was just quickly writing something up so I just did whatever worked.

However, the thing I needed the extra settings for turned out not to be required.

But if in the future more things need to be passed between the scripts, this PR can be used. Just need to :

• Remove the "path ID override" function, I don't think we will end up using it in the future
• Pass JSON via stdin? unsure how other command line programs normally do it. I guess the temp file method works fine, though.