our local Armadillo change with an alt. rng is now an RcppArmadillo header
Armadillo 4.450.1 with support for an alternative RNG
support new alternative RNG scheme falling back to R
update DESCRIPTION to reflect Armadillo 4.450.1 and RcppArmadillo 0.4.450.1.0

this contains Conrad's accomodation of the RNG provided by R
Merge pull request #21 from RcppCore/feature/alt-rng

Feature/alt rng