While investigating something unrelated I stumbled across the `*_setup`
functions, and I noticed that they contain a lot of code that looks like this:

```c
self->abc = NULL;
self->xyz = NULL;
// ...
```

Something told me that assigning `NULL` to a bunch of fields is propably not
needed, and when looking at the docs for `tp_alloc()` I found this reference to
[`allocfunc`](https://docs.python.org/3/c-api/typeobj.html#c.allocfunc), the
typedef for `tp_alloc()`:

> It should return a pointer to a block of memory of adequate length for the
> instance, suitably aligned, **and initialized to zeros**, ...

Emphasis is mine.

Basically I added a simple check that removes lines similar to above which
assigns `NULL` values in setup functions. This removes about ~4100 lines from
the C file when self-compiling.