Create initial version of setup.py

[jankrepl]

Goal

Make this repository installable

pip install git+https://github.com/allenai/scibert.git

Closes #83

Important notes

• The @ syntax requires pip>=19.1
• Fixed the version to 0.1 (semantic versioning)
• The scripts and data folders are not included during installation. This means one could only use it for inference. To address this problem in the future I would suggest creating entry_points for the scripts. One could use data_files for the data folder.
• I wanted to use the official allennlp branch since https://github.com/allenai/allennlp/pull/3537 introduced the gradient accumulation feature. However, the merged commit is only available in the new major releases (1.x.x) and it breaks the scibert code. Therefore I gave up and use the fork https://github.com/ibeltagy/allennlp@fp16_and_others instead (as done currently in requirements.txt)

[ibeltagy]

As you said, the upgrade to AllenNLP v1.x.x is not straightforward. We might give it a try later.