Improved handling of exceptions

[MatthewHambley]

Currently rules tend to carry their own exceptions. This makes a certain amount of sense but there are problems when exceptions get complicated. For instance, if you wanted to enforce kind on immediate values but only when they are present as procedure arguments.

It's hard to argue that the "naked immediate" rule should understand that exception, it's far to specific to a particular requirement.

Some sort of generic exception framework may be the solution but such a thing would likely have to be quite powerful as it probably needs to understand the parse tree.