This is another bug-fix version related solely to a build failure on Windows. Trying to protect paths with spaces has the side-effect of breaking backticks use, which unfortunately is already in use by a number of package that since broke during CRAN autobuilds. No other changes were made.
As always, full details are in Rcpp Changelog page and the Rcpp page which also leads to the downloads, the browseable doxygen docs and zip files of doxygen output for the standard formats. A local directory has source and documentation too. Questions, comments etc should go to the rcpp-devel mailing list off the R-Forge page