Create Jupyter notebooks of examples; demo via Colab

[slivingston]

Colaboratory is able to perform a full installation of TuLiP including optional dependencies such as GLPK.

This task is to create Jupyter notebooks corresponding to the examples. Then, in the documentation, provide URLs to Colab that render directly from this GitHub repository.

If the user has an account with Google, then they can edit the example and run it on Colaboratory.

temporary demo: https://colab.research.google.com/drive/1zaw8st52bUIvdh2aYHxVuOcHRxXfXBYa

[slivingston]

as of today (2019-10-28), the temporary demo URL in the OP continues to work, and I am able to execute the example. the output appears reasonable, but I did not check it carefully.

[slivingston]

somewhat related to this issue: another proprietary competitor in the space of in-browser IDEs is repl.it. they support embedded Matplotlib plots, and recently they released support to create Repl environments from GitHub repositories.

unlike Colab, repl.it is built around a code editor and terminal, instead of an interactive notebook (e.g., as in Jupyter).

so, we might consider making examples also in repl.it

[slivingston]

For Jupyter notebooks, there is also Binder, which is open source.

[slivingston]

progress in #224