Return using Exception not return_points.

[Pebaz]

Returning from a function may work, but it is inconsistent and uses something that is not similar to a loop. If an error is created named ReturnError that holds the Value to return, it can escape any number of loops to return a value.

This may not be worth the effort to implement, but would simplify the inner-workings of LambdaCore and help the programmer's mental model when adding features.