Release v2.9.0

• Support dependency-less generators. (#193)
• Implement custom console/streams (#190)
• Environment#run() returns a promise, unless with help option.
• Reimplement promise returned by Environment#run().
• Support for prompt with prefilled answers.
• Implement Environment#getVersion for api/feature check.
• Create a shared mem-fs-editor, so it can be removed from generator dependency.
• Lookup for ts generators.
• Update dependencies.
• Fix security warnings.
• Some experimental features.