Do not load ruby files in project root (Fixes #269)

This fix results in 2 changes that I'd like a couple of thoughts on.

1. It will never load files in the current directory, unless it is explicitly required or passed as a path.

2. `Cucumber::Cli::Configuration#paths` no longer includes the default 'features' dir, it just returns the paths passed by the user. We add the default directory in where we need