VkNonDispatchableHandle should be an unsigned sixty-four bit integer, not a signed one

[zacharycarter]

• 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

[oakes]

Fixed here nimgl/vulkan#5