The future of runtime type assertions in node-groupme

Type assertions are great for making sure that our (homemade) types are accurate and fully in sync with what the API sends and expects from us. However, there's a case to be made against validating json structures during runtime.

I would appreciate any feedback/suggestions as to whether we should continue using type checkers since it is a major design decision both for node-groupme and for the [groupme-api-types](https://github.com/not-so-smart/groupme-api-types) repository.

### Pros
- Ensures that runtime data fulfills compile-time assumptions made on that data (i.e. you can be confident when intellisense says a field/property will exist in your code)
- Makes debugging easier by pinpointing type errors to their root source (the api response) rather than letting something slip through with an unexpected type and causing unexplainable problems later
- Most importantly, helps to improve our type definitions by throwing errors when they are incorrect.

For example, the type of `APIGroup#join_question` is currently set to `null` because my sample set (the groups I was in at the time) didn't have any join questions when I wrote those types. As a result, node-groupme currently throws an error upon trying to fetch groups with a join question set:
```
-----
API request
url: https://api.groupme.com/v3/groups
-----
(node:18316) Error: Invalid value {"type":"join_reason/questions/text","text":"are you a bot?"} for type null
```
This is valuable because it lets us immediately know that the types are wrong and fix them. However, it is worth considering whether this is worth the costs of type checking every single request.

### Cons
- Lots of overhead at runtime to validate objects that are valid 99% of the time; if our types are always correct then checking them is completely redundant
- Workflow/logistical complications -- generating transformers is hard, keeping transformers up to date with types is even harder
- discord.js doesn't do it https://github.com/discordjs/discord-api-types

Currently I am leaning toward discontinuing the transformers as we transition to groupme-api-types. Any thoughts or opinions on this one way or the other are appreciated.