Include development gems, but only if we're not in production. Provides a method (DevelopingGems.gems) that can be invoked in the Gemfile, and one (DevelopingGems.requires) that can be used in the code to require the gems. The standard list of development gems is: - pry - pry-stack_explorer - pry-doc This may be overridden in two ways: - The DevelopingGems.gems and DevelopingGems.requires methods take an optional argument that is an array of gem names, which it will use. - If a $DEVELOPING_GEMS environment variable exists, it will be used. It is expected to be a list of gem names, separated by spaces.