Extra methods for raw pointers and `NonNull<T>`. For example
`.post_inc()` and `.pre_dec()` (c.f. `ptr++` and `--ptr`), `offset` and
`add` for `NonNull<T>`, and the function `ptrdistance`.
This package contains library source intended for building other packages which
use the "default" feature of the "rawpointer" crate.