Use uri instead of path in CucumberFeature

On Windows paths use '\' as separator, but uri:s use '/'. On other
platforms both paths and uri:s use '/' as separator. Make sure that
paths are converted to uri:s when CucumberFeatures are created.
Merge branch 'use-uri-not-path' of github.com:brasmusson/cucumber-jvm
Attribution. Closes #562.