More efficient job search with separation

Let's add another section to https://python.quantecon.org/mccall_fitted_vfi.html

We explain that there is another, more efficieint method and add the following (@HumphreyYang 's version).

https://gist.github.com/jstac/c595f6bb8993245f38dea273b424b709

(It means that the previous lecture could also be done more efficiently --- we could make that an exercise.)