Wasn't able to setup a Vulkan message callback with the current API
* **I'm submitting a ...**
  - [ ] bug report
  - [x] feature request
  - [ ] support request => Please do not submit support request here, see note
  at the top of this template.


* **Do you want to request a *feature* or report a *bug*?**

Feature. 

I've been trying to follow along [this Vulkan tutorial](https://vulkan-tutorial.com/Drawing_a_triangle/Setup/Validation_layers), but doing it all in Nim.  So far it's been not bad, but the `Message Callback` section setup hasn't worked well for me.

Right now, this block of code doesn't compile:

```nim
proc setupDebugMessenger() =    
  if not enableValidationLayers:    
    return    
    
  let createInfo = newVkDebugUtilsMessengerCreateInfoExt(    
    sType = VkStructureTypeDebugUtilsMessengerCreateInfoExt,   #  doesn't exist in `nimgl` right now..., so I can't setup debug message callbacking
    messageSeverity = (VkDebugUtilsMessageSeverityVerboseBitExt.int or VkDebugUtilsMessageSeverityWarningBitExt.int or VkDebugUtilsMessageSeverityErrorBitExt.int).VkDebugUtilsMessageSeverityFlagsEXT,
    messageType = (VkDebugUtilsMessageTypeGeneralBitExt.int or VkDebugUtilsMessageTypePerformanceBitExt.int).VkDebugUtilsMessageTypeFlagsEXT,              # Note: validation bit doesn't exist in nimGL
    pfnUserCallback = debugCallback.PFN_vkDebugUtilsMessengerCallbackEXT,    
    pUserData = nil    
  )    
```
Also having to cast all of the flags to `int`s first to do the bitwise operations, then case them back is quite clunky.  On top of that, constants/defines such as `VK_TRUE`/`VK_TRUE` don't exist, but `VkBool32` is available.  `VK_NULL_HANDLE` is another one.


* **What is the current behavior?**

Doesn't compile


* **What is the motivation / use case for changing the behavior?**

Being able to debug is nice.



* **Please tell us about your environment:**
  - Version: 1.1.3
  - OS:  Linux
  - Bindings:  Vulkan 
  - Backend: C

I was able to compile my code, but not run it until I installed the LunarG Vulkan SDK.  Do I maybe need to have that SDK installed first?  Then when I do the `nimble install nimgl`, it does some system scanning and then adds stuff based on on dev. environment?