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::ParseError
Oj.load("null")
# => nil

JSON.parse("null", quirks_mode: true)
# => nil
JSON.parse("null")
# => Oj::ParseError
```