Add runtime debug testing with appropriate compile flag

[tiehuis]

This is a small addition that really helps when ensuring that one has written the generation steps correctly.

We can perform the following:

• Ensure map and arr calls have the correct number of items within them
• Ensure buffer overflows do not occur

These are not foolproof, especially with buffer overflows as we would need to consider the case where the values inserted are the largest possible and then check that, but it should be a reasonably good first step.

For statically assuring the buffers are large enough, we could provide a macro, say np_size_req which expects a list of np calls and returns the required space needed in the worst case. May not be tremendously helpful though.