Implement an API for users to define their own scripting languages.

[willnationsdev]

This involves integrating peglib as a thirdparty library via NativeScript. With it, someone can just assign a String to it to generate an internal grammar and then call methods on the parser that will parse text according to the described grammar.

This will then make it much easier for people to devise their own scripting languages for integrations like Twine/Harlowe, Ink, RenPy, Markdown/Fountain, etc.