`VkNonDispatchableHandle` should be an unsigned sixty-four bit integer, not a signed one
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* **What is the current behaviour?**
Currently `VkNonDispatchableHandle` is defined as being a sixty-four bit integer

* **Please provide the steps to reproduce and if possible a minimal demo of the problem**
Look at vulkan.nim, line 42

* **What is the expected behaviour?**
According to `vulkan_core.h`, lines 53-59 it should be an unsigned sixty-four bit integer when pointers aren't being used for handles:

```
#ifndef VK_DEFINE_NON_DISPATCHABLE_HANDLE
    #if (VK_USE_64_BIT_PTR_DEFINES==1)
        #define VK_DEFINE_NON_DISPATCHABLE_HANDLE(object) typedef struct object##_T *object;
    #else
        #define VK_DEFINE_NON_DISPATCHABLE_HANDLE(object) typedef uint64_t object;
    #endif
#endif
```

* **Please tell us about your environment**
Not relevant

* **Other information** (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, docs.gl, documentation etc)

The vulkan_core.h header makes this pretty clear that it should be a `uint64` and not a `int64`
