Reduce and rework Vignette

[JustinMShea]

Reduce the size and scope of the vignette to a handful of interesting examples, with better workflows

Considering eliminating it altogether, and reducing package size and suggested packages in the process!

Florian Hess just came out with a 2nd edition of his Using R for Introductory Econometrics book, and its excellent. He offers a far more in depth treatment than this vignette, and should be the go to source for using R to work with the textbook.

[tappek]

If you want to keep/enhance the Appendix about econometric text resources, there is now pull request #8.

Also, you might want to consider to add:

• Hanck/Arnold/Gerber/Schmelzer, Econometrics with R, online book https://www.econometrics-with-r.org/.
• Croissant/Millo, Panel Data Econometrics with R, 2019, John Wiley & Sons, Hoboken.

[JustinMShea]

Thank you for your suggestions, and your pull request.