FEAT: Execute downloaded notebooks

[AakashGfude]

This PR implements the feature to execute notebooks in _downloads folder.
To enable this feature, one has to set jupyter_download_nb_execute variable to True in config

[mmcky]

thanks @AakashGfude

[mmcky]

thanks @AakashGfude this looks great. If you have tested it I am happy to merge.

[AakashGfude]

@mmcky testing on lecture-source-py worked well

[mmcky]

@AakashGfude would you mind to test on julia as well. Thanks.

[mmcky]

@arnavs would you have time to give this branch a try on the julia repo?

[arnavs]

@mmcky Sure, will give this a go in the next few hours.

[mmcky]

@AakashGfude when I tested this on the anu workstation it appears the index.html is writen using url links to lectures.quantecon.org rather than relative links as is the case on the master branch. Can you replicate this?

<li><a href="https://lectures.quantecon.org/multi_agent_models/index.html">Multiple Agent Models</a><ul>
<li><a href="https://lectures.quantecon.org/multi_agent_models/schelling.html">Schelling’s Segregation Model</a></li>

should be more like

<li><a href="getting_started_julia/index.html">Getting Started with Julia</a><ul>
<li><a href="getting_started_julia/getting_started.html">Setting up Your Julia Environment</a></li>

[mmcky]

seems to be a bug when forming index.html using this branch.

[mmcky]

Thanks @AakashGfude this is working well for me now.
@arnavs would you mind doing a test on your end for Julia

[arnavs]

Just started a test on this and make website. Will approve and merge if it looks good.

[arnavs]

Maybe it's just me, but I find two things:

1. The spinning up of the execution (i.e., Starting notebook execution for website and html conversion(if set in config)...) is taking much longer.

2. The notebooks in arnavsood@imp:~/research/quantecon/lecture-source-jl/_build/website/jupyter/executed/dynamic_programming are still referring to _static. So then the images are ?s... and _static is still copied.

I set the conf.py in QuantEcon/lecture-source-jl@a8903e4.

[mmcky]

thanks @arnavs your second point is an issue with Julia and how statics are treated internally in the extension. We have a fix on the aws instance that copies statics to all nested folders at the moment. This PR will fix this in favour of a much more robust implementation of static files: #268

@AakashGfude can you look into the first point raised?

[mmcky]

@arnavs regarding point #1 -- execution will take twice as long with this option enabled as it is running the html set of notebooks and the download set of notebooks. Is there something else that is taking a lot longer?

[arnavs]

@mmcky Maybe that was it. I'm looking through this PR and I don't see anything troublesome, so I'm willing to take the plunge. This will be a great help on the Julia side.

[mmcky]

@AakashGfude we need to update this so that if jupyter_download_nb_execute = True then we copy the executed set of notebooks in jupyter/_downloads/executed to jupyter_html/_downloads/ipynb

[AakashGfude]

@AakashGfude we need to update this so that if jupyter_download_nb_execute = True then we copy the executed set of notebooks in jupyter/_downloads/executed to jupyter_html/_downloads/ipynb

@mmcky done. Testing it now

[mmcky]

thanks @AakashGfude this is looking good now. Once your testing is complete and your happy with it -- let me know and I will merge and release 0.4.4. Please change tag to ready when you're happy.