Use Calli for native calls

[gfoidl]

See UnmanagedCall benchmarks for reference.

[gfoidl]

I'm not sure if I'll do this, as it complicates the code quite a lot.
It would be nicer if the runtime itself can be improved, so the gain is for free.

[gfoidl]

This can be superseeded by the use of C# 9 function pointers, and .NET Core 3.0 NativeLibrary.