updated for Rcpp 0.11.0, corrected skeleton packages

now uses versioned Imports: for Rcpp (>= 0.11.0)
simplied Makevars{,.win} in src/ and inst/skeleton
rewrote / expanded the hello_world example to
 - use Rcpp Attributes
 - included a few more examples for data to/from R
updates RcppArmadillo.package.skeleton to
 - no longer have a namespace argument
 - wited updates settings into DESCRIPTION and NAMESPACE
 - invoke compileAttributes