Generator example group

[simi]

New generator example group and recognizing files under spec/lib/generators as generator example group.

Old require "generator_spec/test_case" works and is backward compatible. Only when you require only generator_spec it will include new example group.

Inspired by

• https://github.com/rspec/rspec-rails/blob/master/lib/rspec/rails/example.rb
• https://github.com/rspec/rspec-rails/blob/master/lib/rspec/rails/example/controller_example_group.rb
• https://github.com/rspec/rspec-rails/blob/master/spec/rspec/rails/example/controller_example_group_spec.rb

[simi]

@parndt thanks for review. I fixed it and pushed.

[simi]

@parndt issue description updated with backward compatibility note.

[simi]

I think this is ready to merge folks.

[parndt]

Cool @stevehodgkiss how do you feel about it? Looks alright to me!

[stevehodgkiss]

Yeah seems reasonable. :+1:

[parndt]

Perfecto

[simi]

awesomio