Memory management for Gens on the PARI stack or the heap

class cypari2.stack.DetachGen

Destroy a Gen but keep the GEN which is inside it.

The typical usage is as follows:

1. Creates the DetachGen object from a :class`Gen`.
2. Removes all other references to that Gen.
3. Call the detach method to retrieve the GEN (or a copy of it if the original was not on the stack).