Add predefined link flags to .cabal

  - now links to Netlib Blas by default
  - predefined flags are added for common use cases
  - still needs some manual intervention
Update .travis.yml

  - always show output of tests on Travis
  - run tests in tarball as well to avoid missing modules

Note: tried to test against OpenBLAS as well but Travis failed with
"Illegal instruction" even though the linking went successfully.  Unable
to reproduce locally on virtual machine.
Update readme and package description