Generate stats.json

The tool currently generates stats.txt, which is outdated and does not work. Please update it to generate stats.json. 
Example of conversion from stats.txt to stats.json: 
https://github.com/Detanup01/gbe_fork/commit/bc4aa8ff0daaee94aae36c9c438912ebfbb621e3 
and a PR:
https://github.com/Detanup01/gbe_fork/pull/205