move tests with external dependencies to separate category

* split off functional tests with dependencies on external components
  (e.g. RethinkDB) into a separate group (dubbed integration tests),
  to make it easier to run all other tests in non-Eleven environments
* add "alltests" npm script as a shortcut for lint+test+functest+inttest
* README updates
remove npm run-script arguments workaround

As of v2.0.0, npm supports arguments for scripts.
Merge pull request #12 from yelworc/split-tests

split up functests into functional and integration tests