Changed "xhistogram" to "histogram" and other light edits.
Found trouble with "cor()", and will commit this for now (but we need to fix cor()!)
Merge branch 'beta' of github.com:rpruim/mosaic into njh002
Merging beta.
Merge branch 'beta' of github.com:rpruim/mosaic into njh002
Updated NEWS with new vignettes; added placeholder for Compendium of Commands.