[Rd] Rcpp -> RcppTemplate package with L-GPL

[Dominick Samperi]

The R package previously named Rcpp has been renamed to
RcppTemplate (version 1.4), and it is on its way to CRAN.

This is clearer because now RcppTemplate is an R package,
RcppExample is a sample R function, and Rcpp is a C++
class library.

The new package contains the Rcpp class library released
under L-GPL instead of the more restrictive GPL, and it has
been reorganized so that it can be used like a template for
creating R packages that use C++ libraries.

In particular, the Rcpp source files have been moved from src to
inst/lib, and the static library libRcpp.a is built as part of the package
install process. It is linked against when building the package
shared library and then deleted.

See the latest RcppAPI.pdf file for more information. To view it
use vignette("RcppAPI"), or simply fetch the PDF file from
RHOME/lib/RcppTemplate/doc/RcppAPI.pdf.

Be sure to remove the old package named Rcpp if present, because
otherwise there will be two vignettes named RcppAPI, and this
confuses vignette() (chokes under Windows).

Dominick