#2442: Added new interpreter as described above. The new function symbol accepts lambdas in the constructor and gets intitialized with a fixed arity. The MethodInfo of the provided lambda is stored internally and used by the interpreter. The MethodInfo field should be [Storable] but this would require a small change to the serializer (relatively trivial I think). Currently it works with the programmable problem and the SymbolicExpressionTreeEncoding (see attached example).