Changed the layout of tables to markdown syntax

[kolibril13]

More intuitive, and will give better result when rendering with nbsphinx.

[zivy]

For some reason this change isn't compatible with the testing code (fails on this line). Not sure if this is worth looking into as both html and md are fine. 99% of the people using the notebooks will never be aware which is being used in the text cells.

[kolibril13]

Maybe we can then remove that test?
Becuase nbsphinx will render these markdown flavoured tables nicely: https://nbsphinx.readthedocs.io/en/0.8.6/markdown-cells.html#Tables
https://raw.githubusercontent.com/spatialaudio/nbsphinx/0.8.6/doc/markdown-cells.ipynb

[zivy]

I'd rather not remove that test, as it is ensuring that there are no broken urls in the text cells. I can invest a bit of time looking into this, but that will be during the weekend. Worst case, if there is no solution I can disable the test for this notebook, similar to what we did here.