Update to the latest stable release. The main changes are:

• expanded qr() to optionally use pivoted decomposition;
• updated physical constants to NIST 2018 CODATA values;
• added ARMA_DONT_USE_CXX11_MUTEX configuration option to disable use of std::mutex;
• faster handling of matrix multiplication expressions by diagvec() and diagmat();
• added trimatu_ind() and trimatl_ind();
• more consistent detection of sparse vector expressions.