Add Sphinx documentation

Add Sphinx documentation, with

• Display version in the sidebar (like readthedocs, e.g., https://docs.h5py.org/en/latest/quick.html)
• Change color of sidebar title to the icon's grey
• Add the following structure
  • Index: a few sentences to describe the project (taken from README), and a link back to the Gitlab project
  • Quickstart: installation, and example of usage (taken from README)
  • Constant list: constant list as we currently have
  • Reference: API reference of classes
  • Licenses: include LICENCE file (which is now empty)
• Remove the redundant parts from the README, and only leave
  • Quick description
  • Link to the documentation (visible)
  • Contribution guide
  • Contact