CLIP (ViT) (#315)

* probably approximatelly correct CLIPTextEncoder

* implemented CLIPEncoderLayer as built-in nn.TransformerEncoderLayer

* replaced embedding layer with simple matrix

* implemented ViT

* added ViT tests

* fixed tests

* added pooler_output for text

* implemented complete CLIPModel

* implemented init

* implemented convert.py and from_pretrained

* fixed some minor bugs and added the README.md

* removed tokenizer unused comments

* removed unused deps

* updated ACKNOWLEDGEMENTS.md

* Feat: Image Processor for CLIP (#1)

@nkasmanoff:
* clip image processor
* added example usage

* refactored image preprocessing

* deleted unused image_config.py

* removed preprocessing port

* added dependency to mlx-data

* fixed attribution and moved photos to assets

* implemented a simple port of CLIPImageProcessor

* review changes

* PR review changes

* renamed too verbose arg

* updated README.md

* nits in readme / conversion

* simplify some stuff, remove unneeded inits

* remove more init stuff

* more simplify

* make test a unit test

* update main readme

* readme nits

---------

Co-authored-by: Noah Kasmanoff <nkasmanoff@gmail.com>
Co-authored-by: Awni Hannun <awni@apple.com>

README.md

@@ -26,9 +26,15 @@ Some more useful examples are listed below.
 
 - Speech recognition with [OpenAI's Whisper](whisper).
 
+### Multimodal models
+
+- Joint text and image embeddings with [CLIP](clip).
+
 ### Other Models 
 
 - Semi-supervised learning on graph-structured data with [GCN](gcn).
+- Real NVP [normalizing flow](normalizing_flow) for density estimation and
+  sampling.
 
 ### Hugging Face