Add mode for creating a new theory file

[Twigonometry]

Add an interactive mode to the script that allows user to say "I wish to create a new DSL specification in X language with Y filename"

• we create a Y.thy file for them, that already imports StringUtils (perhaps with comments guiding them how to write it)
• we create a boilerplate file with Y_boilerplate_X.txt naming convention
• we create a Y_pp_X.thy file for them to add their pretty-print function (perhaps with comments guiding them how to write it)

[Twigonometry]

Relucantly adding this to Further Improvements milestone. I think this feature will be easy to implement, but perhaps not as high priority as some other enhancements. It will definitely be discussed in the further work section if not implemented.