Closes #502 (#503)

* Initial head qa dataset

* Removed t2t schema

* refactor: Refactor HEAD-QA dataset implementation to hub-based schema

* Minor adjustments to Readme

---------

Co-authored-by: Mario Sänger <[email protected]>
Co-authored-by: Florian Borchert <[email protected]>

bigbio/hub/hub_repos/head_qa/README.md

@@ -0,0 +1,50 @@
+---
+language:
+  - es
+  - en
+bigbio_language:
+  - English
+  - Spanish
+license: mit
+bigbio_license_shortname: MIT
+multilinguality: multilingual
+pretty_name: HEAD-QA
+homepage: https://aghie.github.io/head-qa/
+bigbio_pubmed: false
+bigbio_public: true
+bigbio_tasks:
+  - QUESTION_ANSWERING
+---
+
+
+# Dataset Card for HEAD-QA
+
+## Dataset Description
+
+- **Homepage:** https://aghie.github.io/head-qa/
+- **Pubmed:** False
+- **Public:** True
+- **Tasks:** QA
+
+HEAD-QA is a multi-choice HEAlthcare Dataset. The questions come from exams to access a specialized position in the 
+Spanish healthcare system, and are challenging even for highly specialized humans. They are designed by the 
+Ministerio de Sanidad, Consumo y Bienestar Social. The dataset contains questions about following topics: medicine, 
+nursing, psychology, chemistry, pharmacology and biology.
+
+
+## Citation Information
+
+```
+@inproceedings{vilares-gomez-rodriguez-2019-head,
+    title = "{HEAD}-{QA}: A Healthcare Dataset for Complex Reasoning",
+    author = "Vilares, David  and G{\'o}mez-Rodr{\'i}guez, Carlos",
+    booktitle = "Proceedings of the 57th Annual Meeting of the Association for Computational Linguistics",
+    month = jul,
+    year = "2019",
+    address = "Florence, Italy",
+    publisher = "Association for Computational Linguistics",
+    url = "https://www.aclweb.org/anthology/P19-1092",
+    doi = "10.18653/v1/P19-1092",
+    pages = "960--966"
+}
+```