implement LoRA / QLoRA (#46)

* implement LoRA / QLoRA

- example of using MLX to fine-tune an LLM with low rank adaptation (LoRA) for a target task
- see also https://arxiv.org/abs/2106.09685
- based on https://github.com/ml-explore/mlx-examples/tree/main/lora

* add some command line flags I found useful during use
- --quiet -- don't print decorator text, just the generated text
- --prompt @/tmp/file.txt -- load prompt from file

* user can specify path to model OR model identifier in huggingface

* update mlx-swift reference

Co-authored-by: Ashraful Islam <ashraful.meche@gmail.com>
Co-authored-by: JustinMeans <46542161+JustinMeans@users.noreply.github.com>

mlx-swift-examples.xcodeproj/project.xcworkspace/xcshareddata/swiftpm/Package.resolved

@@ -16,7 +16,7 @@
       "location" : "https://github.com/ml-explore/mlx-swift",
       "state" : {
         "branch" : "main",
-        "revision" : "b4d3e4bbbe41e6dc7c46d5ba075049ae7177961b"
+        "revision" : "cf2c5d20c8575b375cb0d97a06ae0199527b5f32"
       }
     },
     {