PR - first simple implementation

Usage:

```ruby
class Test
  include Configify
  
  configuration do
    env_variable_prefix :TEST
    
    property :play, default: 123
  end
  
  attr_reader :play
  
  def initialize config: config
    @play = config.play
  end
end

t = Test.with_config 

# or load env 

t = Test.with_config do |config|
  config.load_from_env
end
```