Vignettes with Chapter Content

[lachlandeer]

Goal is to add vignettes that provide R code and output for each Chapter's Examples:

• [x] Chapter 1.7: Returns to Scale in Electricity Supply
• [x] Chapter 2.11: Rational Expectations Econometrics
• [x] Chapter 3.9 Returns to Schooling
• [ ] Chapter 4.7: Interrelated Factor Demands
• [ ] Chapter 5.4: International Differences in Growth Rates
• [ ] Chapter 6.8: Forward Exchange Rates and Optimal Predictors
• [ ] Chapter 9.6: Purchasing Power Parity
• [ ] Chapter 10.5: Demand for Money in the United States