* Fix installation on non-UTF-8 platforms

Installation was broken on Windows,
because of non_ASCII characters in the README.

* Add Github actions for testing/coverage

Make sure that python-louain is installed for coverage.

* Remove travis

* Support Python versions 3.8-3.11

* Fix pytest deprecation warnings

We got a bunch of warnings in CI like this:

   tests/test_linkpred.py::TestLinkpred::test_predict_all
    /home/runner/work/linkpred/linkpred/.tox/py/lib/python3.11/site-packages/_pytest/fixtures.py:917: PytestRemovedIn8Warning: Support for nose tests is deprecated and will be removed in a future release.
    tests/test_linkpred.py::TestLinkpred::test_predict_all is using nose-specific method: `teardown(self)`
    To remove this warning, rename it to `teardown_method(self)`
    See docs: https://docs.pytest.org/en/stable/deprecations.html#support-for-tests-written-for-nose

* Add ruff and fix a bunch of ruff warnings

* Fix various deprecation warnings

This introduced a bug during development (sparse matrix vs sparse
array).
Since scipy 1.10, the power operator ** performs elementwise
multiplications, instead of matrix multiplication. In this change, we
implement a small recursive function to reinstate the old behaviour,
such that the Katz predictor can rely on it again.

Fixes #37

* Bump dependency versions

* Update badges to refer to GH Actions rather than Travis
* Correctly reflect the Python versions supported

"Checking dist/linkpred-0.6-py3-none-any.whl: FAILED
ERROR    `long_description` has syntax errors in markup and would not be
         rendered on PyPI.
         line 14: Warning: Explicit markup ends without a blank line; unexpected
         unindent.
Checking dist/linkpred-0.6.tar.gz: FAILED
ERROR    `long_description` has syntax errors in markup and would not be
         rendered on PyPI.
         line 14: Warning: Explicit markup ends without a blank line; unexpected
         unindent."

Fixes #42 (hopefully)