add .travis.yml file

Simple .travis.yml file, which runs the default tests.  Still requires
setting up build hooks in github.
sync up changes with master

Rebase to master, after changes to the function interfaces were merged
in.
Merge branch 'master' into add-travis-ci
Update .travis.yml

This travis file will build and test floats using both release and tip,
and then ensure that the code is properly formatted.  If any tests
fail, it will currently just email me.

The email list should be expanded, but I didn’t want to “volunteer”
people to keep an eye on this package.
Merge pull request #13 from gonum/add-travis-ci

Add .travis.yml