By moving the top-level file armadillo to the two 'versioned' directories
current/armadillo // for 15.0.1 or later
legacy/armadillo // for 14.6.3
we removed the abity to call #include <armadillo> -- as RcppArmadillo-using packages should of course call the headers proving RcppArmadillo where Armadillo is implicit.
That, a few dozen packages called #include <armadillo> directly (even if most likely they should not) so we will restore that entry point and branch to 'current' and 'legacy' as we do via the default headers of the RcppArmadillo package.