Add GPTJ Support

[jamesdborin]

Thanks for all the work making this repo easier to extend.

Starting the process early with a gptj implementation.

Running this gives the following eval results:

4-bit:

Task	Version	Metric	Value
wikitext	1	word_perplexity	11.1044
		byte_perplexity	1.5686
		bits_per_byte	0.6495

fp16:

Task	Version	Metric	Value
wikitext	1	word_perplexity	10.8818
		byte_perplexity	1.5627
		bits_per_byte	0.6440

Let me know if there's anything you would like to see in terms of formatting

[casper-hansen]

Results look good to me. Just need to update the max_new_tokens_key to n_positions. This variable helps us look into the config provided with the model to update to the correct sequence length.

[jamesdborin]

A note:

To get gpt-j to work I had to change the input variable in Catcher in models/base.py from inp to hidden_states. This is because the forward method of GPTJBlocks pass hidden_states by keyword but most huggingface models pass by position. This shouldn't affect the other models because they are passed in by position, which is why inp worked.

However this might cause conflict in the future if other models pass by keyword with a different name...

[casper-hansen]

Thanks @jamesdborin for the PR. I simply renamed the inputs before merging. GPTJ support added, which is nice to see.