Description
As noted in #124 and #123 we currently have a bad situation with useful error messages and input checks in general.
I like very much how this is done in React. The error messages in it are very detailed and contextual. They describe what you done wrong, where to look at, and how to fix the issue.
Also React has a lot of deprecation warnings, so basically if your app has no complaints of deprecations, the switch to the next major version should be pretty smooth.
Also React has two builds for development and production, and production build has zero warnings and no checks itself (which is good for performance). Frankly I'm a bit speculating here, and not sure what is actually cut in the production build of React.
I think we should also have two builds like that. A thing to note here is that react is mostly frontend library, while Kefir may be usable in backend as well. I don't have much experience with backend development, and not sure what would be the best approach of controlling warning/errors for backend.
In Kefir there is a huge room for improvement here. We should chose a strategy, and then just work in this direction one step at a time. I'd borrow most of ideas from React, although maybe we'll need to adjust them for server side usage case.