[Python-Dev] Devguide document on PEG parser

Hi, After some effort, I just finished a new extensive document in the devguide regarding how to use the new PEG parser and the PEG grammar: https://devguide.python.org/parser/ The document contains descriptions, backgrounds, references, guides, and tips. Ideally, this will make it a bit easier for everyone that wants to deal with the grammar or the parser. Hope that you find it useful :) P.S. Thanks to everyone that helped with the review! Regards from cloudy London, Pablo Galindo Salgado