openblas: Replaced head by working commit. Removed TARGET specification (seems to be working without it).
README_openblas: Added README to for openblas to explain TARGET specification and point to further information.
README_openblas: Added more details about default TARGET (NEHALEM) and a link to a list of architectures options for TARGET in the OpenBLAS repo. Broke up the contents a nicer more reader friendly way.