Doc styler examples (#14953)

* Fix bad examples

* Add black formatting to style_doc

* Use first nonempty line

* Put it at the right place

* Don't add spaces to empty lines

* Better templates

* Deal with triple quotes in docstrings

* Result of style_doc

* Enable mdx treatment and fix code examples in MDXs

* Result of doc styler on doc source files

* Last fixes

* Break copy from

docs/source/model_doc/gpt_neo.mdx

@@ -29,16 +29,24 @@ The `generate()` method can be used to generate text using GPT Neo model.
 
 ```python
 >>> from transformers import GPTNeoForCausalLM, GPT2Tokenizer
+
 >>> model = GPTNeoForCausalLM.from_pretrained("EleutherAI/gpt-neo-1.3B")
 >>> tokenizer = GPT2Tokenizer.from_pretrained("EleutherAI/gpt-neo-1.3B")
 
->>> prompt = "In a shocking finding, scientists discovered a herd of unicorns living in a remote, " \
-...          "previously unexplored valley, in the Andes Mountains. Even more surprising to the " \
-...          "researchers was the fact that the unicorns spoke perfect English."
+>>> prompt = (
+...     "In a shocking finding, scientists discovered a herd of unicorns living in a remote, "
+...     "previously unexplored valley, in the Andes Mountains. Even more surprising to the "
+...     "researchers was the fact that the unicorns spoke perfect English."
+... )
 
 >>> input_ids = tokenizer(prompt, return_tensors="pt").input_ids
 
->>> gen_tokens = model.generate(input_ids, do_sample=True, temperature=0.9, max_length=100,)
+>>> gen_tokens = model.generate(
+...     input_ids,
+...     do_sample=True,
+...     temperature=0.9,
+...     max_length=100,
+... )
 >>> gen_text = tokenizer.batch_decode(gen_tokens)[0]
 ```