Add command line argument handling for running single scenarios in features

Like other cucumber implementations, it would be nice to be able to run just a single scenario in a large feature file using the command line argument pattern featurefilename.feature:linenum.

This involved making sure any "expandPaths" calls could ignore, yet preserve, the line number suffix, so that once the feature file source is loaded, the parser has access to the scenario.getUri() with the specified line number (if any). Then an astFilter can simply include or exclude scenarios if a line number was passed.

I had to fix one unimplemented (mislabelled) step in cli_steps.js and also apply the patch in issue #120 / #123 because the stdout not being fully flushed causes the cli.features to fail.

Look forward to any feedback.

Cheers
Simon