Document runtime error handling

[Akuli]

I think the best way to handle errors in Jou is:

• return special values (e.g. NULL or -1) in stdlib
• use assert in quick and dirty scripts (e.g. AoC solutions)
• use a custom error handling function in larger projects (e.g. Jou compiler).

Advantages:

• Super simple
• Requires no special features in language/compiler
• User chooses how to handle errors

Disadvantages:

• No standard way to get a human-readable error message string
• No compiler warning if you forget to handle error case

This seems like a reasonable tradeoff for Jou, even though it's not a good solution in most other languages. It's also basically what C does.

This should be documented.

[Moosems]

Will there be a way to try/except for assertion errors?

[Akuli]

No