Add support for the language from the [Railroad-diagram Generator](https://tabatkins.github.io/railroad-diagrams/generator.html) as input. Example: ``` Diagram( Optional('+', 'skip'), Choice(0, NonTerminal('name-start char'), NonTerminal('escape')), ZeroOrMore( Choice(0, NonTerminal('name char'), NonTerminal('escape')))) ``` Online: https://tabatkins.github.io/railroad-diagrams/generator.html Format documentation: https://github.com/tabatkins/railroad-diagrams#components