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
Interesting. Never thought about this.

Would you put everything into one line?

```ruby
MultiJson.encode object, pretty: params[:pretty] == 'true' || Config.pretty_json
```

Or like this?

```ruby
MultiJson.encode object, \
  pretty: params[:pretty] == 'true' || Config.pretty_json
```

Or with braces?

```ruby
MultiJson.encode(
  object,
  pretty: params[:pretty] == 'true' || Config.pretty_json
)
```

There's no comment in https://github.com/bbatsov/ruby-style-guide about this.

In the end, I do it how it is default in RubyMine. In this case.