Setup `npm test` script.

This commit adds `jasmine-node` as to `devDependencies` and removes the
`tests/runner.sh` script. Now tests can be run from the projects root
directory with `npm test`.

`npm test` is the default test script used by Travis for Node projects.
Merge pull request #6 from rjackson/add_npm_test_functionality

Setup `npm test` script.