added PP_gpcm
1) added examples
2) added description
3) added 2 new functions
added gpcm examples
jk
fix the build bug
1) jk examples
2) SE for jk - but it is significantly lower than the SE which results from MLE/WLE estimation
1) plausible values
2) jackknife
3) now anything is created by roxygen2
4) more examples