Proposal for increasing interface readability

[MirkoCovizzi]

My proposal is to add type aliasing for *mut c_void in the context of interface methods.
Example:

type IParamValueQueuePtr = *mut c_void;

#[com_interface("A4779663-0BB6-4A56-B443-84A8466FEB9D")]
pub trait IParameterChanges: IUnknown {
    unsafe fn get_parameter_count(&self) -> i32;
    unsafe fn get_parameter_data(&self, index: i32) -> IParamValueQueuePtr;
    unsafe fn add_parameter_data(&self, id: *const u32, index: *mut i32) -> IParamValueQueuePtr;
}

The reason for this is that we necessarily need to have these methods return a *mut c_void otherwise it's impossible to cast a fat pointer (like dyn IParamValueQueue) to a thin pointer. By introducing these type aliases we keep the semantics of the method intact (so we know what type is returned by reading the alias name). An alternative can be to use docs, but I feel like this approach is more immediate and requires less noisy information.

[robbert-vdh]

This has been taken care of with the pointer changes from #45. Every pointer argument or return value can now be upgraded to a smart pointer type with the correct semantics.