Pretraining and Fine-tuning Longformer : Increase token limit

@ibeltagy Many thanks for sharing with the community Longformer! (and for all the details you are having in all the Issues section)

I have also a few questions :
**Q1:**
if I want to pretrain Longformer-base-4096, with my custom dataset, but let's say, I set a limit bigger than 4096, (e.g 10k) when I will use the resulted model for fine-tuning ( text classification), I will still be limit to 4096 tokens ?

( background : I have a patent dataset from USPTO , and I want to do text classification on the class of a patent. But the average length of the words in my datasets is around 30k . The minimum length is 1000 and the maximum si 100k words)

**Q2:**
just for the pretraining part, do I need to use the "convert to long" notebook?
https://github.com/allenai/longformer/blob/master/scripts/convert_model_to_long.ipynb

Or I can use just the "How to train" notebook from HF ? https://colab.research.google.com/github/huggingface/blog/blob/master/notebooks/01_how_to_train.ipynb

**Q3:**
Is feasible to create a "long" version of XLnet ?