- Made the use of `const` and `let` consistent
- import required functions and types from 'react' instead of using the
`React.` namespace.
- Added `Expand` type, which can expand complex types to their "final"
result.
- Ensured that we use `as const` for DEFAULT_XXX_TAG where we used a
string. So that we have the type of `div` instead of `string` for
example.
- Used `interface` over `type` where possible. I'm personally more of a
`type` fan. But the TypeScript recommends `interfaces` where possible
because they are faster, yield better error messages and so on.
Robin Malfait