Rebase and merge Louismartin/camembert
Please, continue the comments [here](https://github.com/huggingface/transformers/pull/1822#issuecomment-558095282)

> Great work!
> 
> Could you show how to get the embedding vector of a sentence please?
> 
> ```python
> from transformers import CamembertTokenizer
> import torch
> 
> camembert_tokenizer = CamembertTokenizer.from_pretrained("camembert-base")
> 
> camembert_tokenizer.encode("Salut, ça va ?") # How to get embedding of this sentence not just the ids of tokens ? 
> ```