update continental extension cookbook

[naliboff]

This PR updates the continental extension cookbook to use a number of features that improve the (1) performance (speed) and accuracy of the simulation and (2) make the PRM file easier to read. While I have additional changes in mind, my plan is to do them in a piecemeal fashion, rather than all at once to make things easier to review.

• [x] I have followed the instructions for indenting my code.
• [X] I have tested my new feature locally to ensure it is correct.
• [ ] I have created a testcase for the new feature/benchmark in the tests/ directory.
• [ ] I have added a changelog entry in the doc/modules/changes directory that will inform other users of my change.