Enable Source Distribution

[AntoinePrv]

Steps for PyPI:

• Make Conan optional Installation without conda and conan #121
• Add top level setup.py
• Use sciki-build to drive compilation with CMake
  • Set current version of Python
  • Extract compile flags from setuptools (or scikit-build?)
• Use pyproject.toml and PEP518 to resolve build time dependencies
  • Scikit-build (and CMake)
  • Conan (will resolve libecole dependencies) or CMake FetchContent
  • PyBind11
  • Numpy
  • Scip (unknown so far)
  • xtensor-python (no plan so far availability on pypi xtensor-stack/xtensor-python#219)
• Add Manifest.in
• Use setuptools tests_require=["pytest", "pyscipopt"] for pytest
• Remove dependencies from Dockerfile.src
• Edit conda recipe to use new setup (--no-build-isolation)
• Add a convenient way to run tests (Ctest ?)
• Document how to used development version (PYTHONPATH)
  • Seems not yet supported, should read environment varaibles
• Document how to set SCIP_DIR using pip
• Fix install Rpath
• Add sdist releases to Pypi

Additionally

• Switch to tox for automated testing