improvements to Rcpp.package.skeleton()

* when available, pkgKitten is used to create a better newPkg-package.Rd file
* default license changed from 'What license is it under' (which does not
  pass R CMD check) to 'GPL (>= 2)' which does
* with this pkgKitten becomes a new Suggests:

and the net result is that we now pass 'R CMD check' for skeleton packages
without any notes, warnings or what have you comments
add a (temp.) local copy of pkgKitten::playWithPackageHelpPage()

to be replaced once pkgKitten is updated on CRAN
remove local copy of pkgKitten::playWithPackageHelpPage()

- updated pkgKitten is now on CRAN
- also update DESCRIPTION with versioned Suggests
Merge pull request #176 from RcppCore/feature/use-pkgkitten

Feature/use pkgkitten