Allow Recursion

[mmoult]

If we want to be spec compliant as we say, we should allow for recursion. Data must exist in the data array, not any stack frame, but we can have a list of ids in the stack frame which can be popped off at the OpReturn. We can also have a Stacked Data type which holds the bottom Data and the top Data (at the return, we pop off the top data and replace the Stacked with its bottom).

This will take some refactoring, but should be fairly straightforward.

[mmoult]

Completed in this commit:
a521c1d