Use latest Rubies on Travis
Use cucumber to run integration tests from RSpec
Run features on Travis
Fix `assert_include`
Update around_spec.feature

See https://raw.githubusercontent.com/rspec/rspec-core/c46827984825e9596405658621d8ecfe8ecdf5ff/features/hooks/around_hooks.feature
Swallow arguments passed to around in spec

Try to imitate RSpec's `around(:example)`.
Modify RSpec feature to pass MT's specs
Mark problematic/incompatible features
Let most RSpec features pass