added travis CI config

Before merging, you'll need to enable it for the repository.  Instructions are here: http://about.travis-ci.org/docs/user/getting-started/

The build currently fails due to two tests failing:

NMatrix::BLAS complex64 cblas exposes rotg
NMatrix::BLAS complex128 cblas exposes rotg

Are these the current expected failures?

Also, I've set it to test against 1.9.3.  Are there other ruby versions currently being targeted?