Function pointers are difficult to parse in vk.xml

Vk.xml is a nice but there are a couple spots where it is hard to parse, the worst being function pointer types definition. Here is an example:

``` xml
typedef void (VKAPI_PTR *PFN_vkInternalAllocationNotification)(
void* pUserData,
size_t size,
VkInternalAllocationType allocationType,
VkSystemAllocationScope allocationScope);
```

Getting the return type of the function and splitting the parameters is tricky, and this is made worse by the fact that a `const` can appear before the `` tag.

I suggest using the same structure as `` tags that clearly separate the prototype (and return type) as well as the parameters:

``` xml

void vkCmdDrawIndirect
VkCommandBuffer commandBuffer
VkBuffer buffer
VkDeviceSize offset
uint32_t drawCount
uint32_t stride

[skipped]


```