Add quirks_mode option for JSON compatibility

JSON.parse allows single JSON values for JSON.parse when quirks_mode option is
given. Allow the same quirks_mode option to be given to Oj as an argument. The
default value for this option is true.


```ruby
Oj.load("null", quirks_mode: false)
Oj.load("null")

JSON.load("null", quirks_mode: true)
JSON.load("null")
```