Support for the Object value type

[rogchap]

As documented here: https://v8.github.io/api/head/classv8_1_1Object.html

The Object class represents the non-primitive data types. ie (Objects, Arrays, Promises, Dates, Regex etc)
Primitive data types where implemented in #59

The main "entry" to the Object should be from the Value struct. ie. val.Object().

This may require a multi-PR as the Object class is quite large, and breaking it down will make implementation and reviews easier.