Splitting questions module

[MatthewBaggins]

• moved everything that modifies coda out of questions.py to question_setter.py, by @ProducerMatt 's suggestion
• added module-level docstrings with command instructions to questions.py and question_setter.py and build_help.py, which renders a markdown from them
  • also, added screenshots that show how Stampy reacts to various question-related commands
• refactored these modules
• added lots of tests to questions.py
• removed class_name attribute from individual Module subclasses and added it to the parent class as a property
  • as a result of that, some __init__s were no longer necessary because now they contained only super().__init__(), which is there by default

[ProducerMatt]

Confirmed working in my fork 👍

[MatthewBaggins]

What's new in each module, rather than merely refactored

question_setter

• Stampy now parses GDoc links from all messages, not just from review requests.
  • Motivation: it was apparently intuitive for reviewers to reply with approve to any message with contained appropriate GDoc links and they surprised when Stampy didn't set the relevant question(s) to Live on site. This puts an end to that surprise.
• Similarly, reviewers can now post one or more GDoc links with approved and it will work just as well.

questions

• Stampy no longer rebuilds questions DF cache every 10 minutes. (thanks Aprillion)
• Standardized command syntax etc, documentation and testing

question_query_utils

I wanted to have a type that would specify a few types of question queries: by (1) title (2) gdoc link(s) (one or more) (3) last question that stampy interacted with (4) specified status and/or tag and/or maximum number of questions that I want to get. Something like Rust's enums would be ideal (see Listing 6.2 here), but Python doesn't have that. So I opted for a way that is very non-pythonic but probably very efficient and type-checker-friendly, i.e., using a union of 2-tuples, where the first element is a string literal specifying a type of query and the second is information specifying that query.