SetDllImportResolver based loading (#603)

 - Modified library loading to be based on `SetDllImportResolver`. This replaces the built in loading system and ensures there can't be two libraries loaded at once.
 - llava and llama are loaded separately, as needed.
 - All the previous loading logic is still used, within the `SetDllImportResolver`
 - Split out CUDA, AVX and MacOS paths to separate helper methods.
 - `Description` now specifies if it is for `llama` or `llava`

Author: martindevans

LLama.Examples/Program.cs

@@ -16,11 +16,14 @@ __       __                                       ____     __
 
     """);
 
+// Configure native library to use
 NativeLibraryConfig
    .Instance
    .WithCuda()
-   .WithLogs(LLamaLogLevel.Warning);
+   .WithLogs(LLamaLogLevel.Info);
 
+// Calling this method forces loading to occur now.
 NativeApi.llama_empty_call();
 
-await ExampleRunner.Run();
+await ExampleRunner.Run();
+