Support for closures (#202)
This introduces the closure operations to the Biscuit language, first with the `.all()` and `.any()` operations to add conditions on the elements of a set.
It is now possible to use expressions with the following format:
```
check if [1,2,3].all($p -> $p > 0);
check if [1,2,3].any($p -> $p > 2);
```
Co-authored-by: Geoffroy Couprie <contact@geoffroycouprie.com>