Improve internal fetching pointers to Vulkan functions to always use vkGetInstanceProcAddr/vkGetDeviceProcAddr
Improve internal fetching pointers to Vulkan functions to always use vkGetInstanceProcAddr/vkGetDeviceProcAddr

No longer refers to statically linked Vulkan functions.
Removed configuration macro VMA_STATIC_VULKAN_FUNCTIONS.
Hopefully will help for #56.

GPUOpen-LibrariesAndSDKs/VulkanMemoryAllocator,GPUOpen-LibrariesAndSDKs/VulkanMemoryAllocator,GPUOpen-LibrariesAndSDKs/VulkanMemoryAllocator