Docs on gh-pages

[alecandido]

Fix gh-pages docs deployment workflow.

Brief description of the workflow:

1. checkout the repo and eko submodule
2. install eko and its dependencies
3. install the module
4. build the docs with sphinx
5. deploy to gh-pages branch only the built html

[alecandido]

Docs currently available at address:

https://n3pdf.github.io/dis/

[alecandido]

Improvements

Further improvements available:

• remove sphinx from install requirements:

install_requires=[
    ...,
    "sphinx_rtd_theme",
    "recommonmark",
    "sphinxcontrib-bibtex",
]

probably a good way to run sphinx can be from its setuptools integration

• simplify eko dependency (this will be easily done once a version of eko will be deployed on PyPI or anywhere)
  • document in eko the dependency on libgsl-dev

Pytest

Even if it is not related to this workflow, just to document 📄 it somewhere:

• introduce a pytest requirement in tests_require