OpenBLAS is an optimized BLAS library

Added symbolic link to install a generic blas library that can be used
by Octave and R.

OpenBLAS has cpu specific targetted assembly code for speed
optimisation.  In most cases, the installation will detect the
correct CPU architecture If you want to specify the architecture
you can define the EXTRAPARAMS environmental variable with
EXTRAPARAMS="TARGET=ZEN" (for AMD Ryzen CPUs)