* Add extension nbsphinx-link: link notebook out of the sphinx root folder to the sphinx project
* Link Notebook custom.ipynb directly from python folder to the sphinx project
* Link Notebook seq_and_func.ipynb directly from python folder to the sphinx project
* Small title fix
* Make interactive graphs visible in readthedocs webpage for seq_and_func.ipynb
* Regenerate outputs for custom.ipynb and remove parts of them
* Add nbsphinx extension for docs
* Add specific ipynb files to readthedocs folder and add links to Nano Tutorials index page
* Disable execution of ipynb notebook
* Remove outputs of two ipynb files
* Rename titles and add navigation texts to seq_and_func.ipynb under readthedocs folder
* Rename titles and add navigation texts to custom.ipynb file under readthedocs folder
