Add "match ... with ..." syntax

[Akuli]

Fixes #617

Example:

match "hello" with strcmp:
    case "hello":
        printf("yass\n")

For now, the match function must return int, so you can't match with e.g. starts_with(). This might actually be a good thing, so that usage of match statement remains quite simple and it's not tempting to make things more complicated than needed.