Add Encode helper

Replacement for https://github.com/interagent/pliny-template/pull/126

Pull Request for template: https://github.com/interagent/pliny-template/pull/132
Right on, was surprised to see this is not covered on that style guide too!

If the one-liner has 80 chars or less I'd definitely go for it, but adding a parenthesis because there are several/complex args:

```ruby
MultiJson.encode(object, pretty: params[:pretty] == 'true' || Config.pretty_json)
```

Otherwise we normally go with the third option, favoring parenthesis instead of the slash because it seems more common and readable, in particular for long method calls.