Cleaning up vignettes and adding content to package Rd file

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/uwgarp@151 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
edit to Performance Measures vignette

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/uwgarp@152 edb9625f-4e0d-4859-8d74-9fd3b1da38cb