Swift

This adds support for generating Swift projects.

Yeah, I know, _finally_.
How about `Hash#merge` instead? Maybe something like:

```ruby
def evaluated_configuration
  initial_configuration.merge(template_groups_configuration)
end

def initial_configuration
  default_configuration
    .merge(user_configuration)
    .merge(local_configuration)
    .merge(@options)
end

def template_groups_configuration
  TEMPLATE_GROUPS.inject({}) do |acc, key|
    acc.merge(key => evaluated_templates(key))
  end
end
```