Inline annotations

There are cases when a user might want to provide an annotation for a custom command or even override (force) a behavior on an existing command. In these cases, writing a full JSON in a custom directory is inconvenient. A more convenient approach would be to provide an _inline_ annotation, which PaSh could read and expand appropriately during its pre-processing stage:

```sh
# bigram_aux_map :: (pure, args[0], args[1:4])
bigram_aux_map() {
#...
}
```

Most annotations will fall under a few distinct categories, and thus expressiveness can be optimized towards the common case—after all, developers can always fall back to the JSON for the full expressive power of the annotation subsystem. This infrastructure and associated annotation economy may accelerate research in annotations.