Sphinx-tabs

♻️ Major refactor of tabs, group-tabs and code-tabs (thanks to [foster999](https://github.com/foster999)):

* Removes hard-coded reStructuredText for group and code tabs, so that this works with other parsers (inc `MyST Markdown`)
* group-tab directive now subclasses `TabDirective` to remove duplicated run code
* likewise, `code-tab` now subclasses `group-tab`
* `TabDirective` and `TabsDirective` now subclass `SphinxDirective` for easier access to directive `env`

🧪 testing infrastructure has now fully moved from unittest to pytest

✨ New features:

* Can now pass `code-tabs` with a second argument (allowing whitespace) to provide an alternative tab label
* `code-tabs` can now use custom lexers, which are added to the sphinx app in `conf.py`

🐛 FIX: Remove `app.add_javascript` use for sphinx v2

`sphinx-tabs` has now moved to the [EBP organisation](https://executablebooks.org) 🎉

Deprecated 🗑

- Python < 3.5 and Sphinx < 2 support dropped

Improved 👌

- Lots of code and CI restructuring (see [EBP Migration (76)](https://github.com/executablebooks/sphinx-tabs/commit/6342ed3f1f7d4cb50891001f26d4e3c4c08ee422))

Fixed 🐛

- Replace `add_javascript` by `add_js` for sphinx>=3 (removes warning!),
thanks to [Daltz333](https://github.com/Daltz333)

- Marked the extension as parallel safe (46)

- Fix bug in Internet Explorer (33)
- Drop support for Python 3.4 (as lxml no longer supports it)

- Support for Sphinx 2
- Update to Semantic UI 2.4.1
- Fix oversize tabs in Sphinx 2 (38)
- Various bug fixes