Automatically derive PEG format from upstream

[palfrey]

Maiden's PEG file is at https://github.com/palfrey/maiden/blob/main/src/rockstar.peg and the upstream one is at https://github.com/RockstarLang/rockstar/blob/master/satriani/rockstar.peg, but because PEG.js and pest disagree on formatting, they're not directly compatible. It should however be possible to automatically convert from one to the other. So far, they were converted by hand and have since been manually updated.