Create executables for generate, lora, server, merge, convert (#682)

* feat: create executables mlx_lm.<cmd>

* nits in docs

---------

Co-authored-by: Awni Hannun <awni@apple.com>

llms/mlx_lm/convert.py

@@ -52,7 +52,11 @@ def configure_parser() -> argparse.ArgumentParser:
     return parser
 
 
-if __name__ == "__main__":
+def main():
     parser = configure_parser()
     args = parser.parse_args()
     convert(**vars(args))
+
+
+if __name__ == "__main__":
+    main()