Create cran-comments.md

Increment version number to 1.7.2

Increment version number to 1.7.1

Increment version number to 1.7.0

Increment version number to 1.6.3

Update .Rbuildignore

Increment version number to 1.6.1

Increment version number to 1.6.0

help file examples updates

prep for v1.5.1 release