Change PhysicalDeviceMemoryProperties to return slices of proper sizes

[GabrielMajeri]

The PhysicalDeviceMemoryProperties struct has functions which allow the developer to get a slice of size VK_MAX_MEMORY_TYPES. The entries up to memory_type_count are valid, the ones after are invalid.

The Voodoo API should have only one function, memory_types, and it should return a slice of the correct size: &memory_types[..memory_type_count].

[c0gent]

Agreed. I'll adjust this as soon as I can.

Please keep the suggestions coming. I won't have time to make these changes right away but having issues filed here is very helpful.