return None when a Some doesn't respond to a method

also wrap result of enumerable methods with Maybe when nil

```ruby
# before
Maybe("Some Value").does_not_exist.or_else{ false }  # NoMethodError
Maybe([]).first.children  # NoMethodError

# after
Maybe("Some Value").does_not_exist.or_else{ false }  # false
Maybe([]).first.children # Maybe::None
```