CRAN release wooldridge v1.4-2

• Reduced scope of vignette, removing examples and Suggested pkgs AER, plm, and prais from the wooldridge DESCRIPTION file. The wooldridge package builds & tests much quicker and cleaner as AER & plm in particular have grown larger dependency trees over the years. prias also has a habit of breaking its API(see notes around release wooldridge 1.3.1), and this has happened yet again in the recent release of praise v1.1.2, triggering wooldridge WARNINGS on CRAN. A helpful note from Prof Brian Ripley was quick to follow, with the usual notification that wooldridge would be removed from CRAN. Given its limited use in an example, it makes sense to remove it all together to avoid future complications. After all, my time as maintainer is limited and this data package should be the easiest of my open source packages to maintain. These Vignette examples are nice, but they are given a much better treatment elsewhere and I refer readers to those sources.

• Added quantmod and xts (very mature and stable packages) to extend a time series example with current data.