add addition feature which uses multiple step files.
move CustomWorld to env.groovy to keep step files pure.
calculator uses stack properly.
add java-like class-based test/demo
add pom.xml with examples of running cuke tests in verify intead of test phase, etc
use mvn to run tests because gradle doesn't like the cucumber junit output
add class showing how cucumber won't work with regular classes in features path
update doc, add smoketest for pre-test check in test phase.