Imperative TypeScript alternative (drastically simpler than TypeScript)

The idea is to allow types to be defined imperatively:

```
type SomeType = {
if (T is string)
return boolean
if (T is SomeOtherType)
return string
return never
}
```

To-do:
- Create a better example that showcases both how much simpler and how much more powerful imperatively defined types would be.
- Create a new TypeScript feature request for it https://github.com/microsoft/TypeScript/issues. Ideally it is the TypeScript team that would add such feature to TypeScript. Otherwise, someone else will eventually create such imperative TypeScript alternative.

Contribution welcome to work on the to-do list above or even create a simple prototype.

No files or tests are identified. Start by refining the imperative type example so it demonstrates the claimed simplicity and power, then review the linked TypeScript issue tracker to prepare a feature request. Done means a stronger example and a submitted TypeScript feature request; a prototype is described as optional.

Written by the indexing model from the issue text.