* applied simple find+sed for 'master' -> 'main'
* Rename master->main in JAX API and internals (#4178)
* Started with #4174
* Renamed Trace.master to Trace.main
* Renamed core.new_master and core.new_base_master
Co-authored-by: George Necula <gcnecula@gmail.com>
Looking at the recent [doc failures](https://readthedocs.org/projects/jax/builds/), a few are due to
- Cell timeouts (which this tries to fix),
- Execution timeout (readthedocs gives 900seconds to build, total -- most of the time for jax is in executing the notebooks),
- Other somewhat random/inscrutable errors (and I could imagine a world in which one of the timeouts ends up triggering an inscrutable error in the execution).
* Moved all notebooks to docs/notebooks.
Now all notebooks are in the same place, thus all are subject
to auto-doc generation at readthedocs.io and to automated testing
with travis.
Some notebooks are too slow, exclude them at docs/conf.py:exclude_patterns.
Cleanup a bit the section headings in notebooks so that they show
up well in readtehdocs.io.
* Increase the cell timeout for executing notebooks
* Exclude also the neural network notebook from auto-generation (timing out)
* Disable the score_matching notebook from auto-doc (travis does not have sklearn)
