expose assertion annotations through `AssertionError` instances

The title is pretty self explanatory. It means that if you have an assertion with annotations, the AssertionError thrown will contain the instances of the annotations' classes.

try
{
    "foo"
    bar baz qux assert(exists obj);
}
catch(AssertionError error)
{
    print(error.annotations);
}

The other day I was just thinking about how useless annotations in assertions are. It feels weird to allow such thing only so you can have the doc annotation there. I thought then: to solve the problem "they don't do anything", instead of disallowing them, why not make them actually do stuff?

[gavinking]

That's an interesting idea.