Add image to README.rst

* Traffic light overview plot

Other changes:
- suppress "matplotlib backend" verbose warning
- click on "popmon report" also scrolls to top
- fix example comment

* Github Actions for building examples as artifacts

Bumps [numpy](https://github.com/numpy/numpy) from 1.18.0 to 1.19.4.
- [Release notes](https://github.com/numpy/numpy/releases)
- [Changelog](https://github.com/numpy/numpy/blob/master/doc/HOWTO_RELEASE.rst.txt)
- [Commits](numpy/numpy@v1.18.0...v1.19.4)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

This reverts commit 518fb37.

* Testing: Change notebook testing to pytest-notebook (current tests were skipped). Add try-except ImportError for pyspark code.

Bugfix in hist.py that broke the advanced tutorial.

Enhancement: Add %%capture to pip install inside of notebooks.

Enhancement: Make package install in notebooks work with paths with spaces.

* Update requirements-test.txt

* Update test_notebooks.py

* Pickle doesn't work with tests (not really a popmon-specific feature anyway). Changed the notebook to fix the issue, left the code for reference.

* Increase timeout

* List talks and articles
* Add Data Lunch

Bumps [numpy](https://github.com/numpy/numpy) from 1.18.0 to 1.19.4.
- [Release notes](https://github.com/numpy/numpy/releases)
- [Changelog](https://github.com/numpy/numpy/blob/master/doc/HOWTO_RELEASE.rst.txt)
- [Commits](numpy/numpy@v1.18.0...v1.19.4)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

This reverts commit 518fb37.

* Testing: Change notebook testing to pytest-notebook (current tests were skipped). Add try-except ImportError for pyspark code.

Bugfix in hist.py that broke the advanced tutorial.

Enhancement: Add %%capture to pip install inside of notebooks.

Enhancement: Make package install in notebooks work with paths with spaces.

* Update requirements-test.txt

* Update test_notebooks.py

* Pickle doesn't work with tests (not really a popmon-specific feature anyway). Changed the notebook to fix the issue, left the code for reference.

* Increase timeout

* List talks and articles
* Add Data Lunch

merge master in develop

…red func

Added proper check of matrix invertibility of covariance matrix in the function relative_chi_squared() in stats/numpy.py

Apparently this check is not propely done by default by numpy.linalg.inv(), see:
https://stackoverflow.com/questions/13249108/efficient-pythonic-check-for-singular-matrix/13264934#13264934

In one of our unit tests we were inverting a non-invertible covariance matrix,
causing maching precision problems (differences) between different systems, causing
the test to fail on some systems, but passing on others.

With a strict invertibility check in place, this test is now fixed and consistent b/n various systems.

Support for the Spark date type (treated as a timestamp).

Extending the unit tests for this type
Install Spark on Github Actions to be able to include spark tests in our CI/CD pipeline
Upgrade linting to use pre-commit (including pyupgrade for python3.6 syntax upgrades)
Document how to run popmon using spark on Google Colab (minimal example from scratch)

Remove nbconvert